feat: Withholding Tax Certificate print format for Purchase Invoice

The Revenue Department's Sec. 50 bis form (approve_wh3_081156.pdf) as
the page background, with the invoice's data positioned in the form's
fields; two copies per certificate. Its AcroForm fields carry no Thai
font, so the PDF is not filled directly.

get_withholding_certificate(doc) resolves the payer and payee (13-digit
tax ID, one-line address), the certificate row from the category's
income_type, the P.N.D. return from the supplier type and income, and
the amounts in company currency with the tax in Thai words. Dates are
Buddhist Era.

default_thai_company/fixtures/print_format.json

@@ -100,5 +100,39 @@
   "report": null,
   "show_section_headings": 0,
   "standard": "No"
+ },
+ {
+  "absolute_value": 0,
+  "align_labels_right": 0,
+  "css": "/* Thai text needs a font with Thai glyphs; ship Sarabun as in Default Standard Sales Invoice. */\n@font-face {\n\tfont-family: \"Sarabun\";\n\tfont-weight: 400;\n\tsrc: url(\"/assets/default_thai_company/fonts/Sarabun-Regular.ttf\");\n}\n@font-face {\n\tfont-family: \"Sarabun\";\n\tfont-weight: 700;\n\tsrc: url(\"/assets/default_thai_company/fonts/Sarabun-Bold.ttf\");\n}\n\n/* The Revenue Department form fills the whole A4 sheet: no page margins. frappe.utils.pdf reads\n   these .print-format properties as the wkhtmltopdf page options. */\n.print-format {\n\tmargin-top: 0mm;\n\tmargin-bottom: 0mm;\n\tmargin-left: 0mm;\n\tmargin-right: 0mm;\n\tpage-size: A4;\n}\n/* On screen the standard sheet padding would clip the 595pt form. */\n@media screen {\n\t.print-format {\n\t\tpadding: 0;\n\t\tmax-width: 595pt;\n\t\tmin-height: 0;\n\t}\n}\n\n/* One sheet per copy; values are positioned in pt against the form's PDF coordinates. */\n.wht-page {\n\tposition: relative;\n\twidth: 595pt;\n\theight: 841pt;\n\toverflow: hidden;\n\tpage-break-after: always;\n\tfont-family: Sarabun, sans-serif;\n\tfont-size: 10pt;\n\tcolor: #000;\n}\n.wht-page:last-child {\n\tpage-break-after: auto;\n}\n.wht-form {\n\tposition: absolute;\n\tleft: 0;\n\ttop: 0;\n\twidth: 100%;\n\theight: 100%;\n}\n.wht-page .f {\n\tposition: absolute;\n\twhite-space: nowrap;\n\toverflow: hidden;\n}\n/* Check mark drawn in CSS: the shipped font has no U+2713 and the PDF renderer sees no system fonts. */\n.wht-page .tick {\n\tposition: absolute;\n}\n.wht-page .tick:after {\n\tcontent: \"\";\n\tposition: absolute;\n\tleft: 4pt;\n\ttop: 0;\n\twidth: 4pt;\n\theight: 8pt;\n\tborder: solid #000;\n\tborder-width: 0 1.5pt 1.5pt 0;\n\t-webkit-transform: rotate(45deg);\n\ttransform: rotate(45deg);\n}",
+  "custom_format": 1,
+  "default_print_language": null,
+  "disabled": 0,
+  "doc_type": "Purchase Invoice",
+  "docstatus": 0,
+  "doctype": "Print Format",
+  "font": null,
+  "font_size": 10,
+  "format_data": null,
+  "html": "{% include \"default_thai_company/templates/print_formats/withholding_tax_certificate.html\" %}",
+  "line_breaks": 0,
+  "margin_bottom": 0.0,
+  "margin_left": 0.0,
+  "margin_right": 0.0,
+  "margin_top": 0.0,
+  "modified": "2026-09-22 09:00:00.000000",
+  "module": "Default Thai Company",
+  "name": "Withholding Tax Certificate",
+  "page_number": "Hide",
+  "pdf_generator": "wkhtmltopdf",
+  "print_format_builder": 0,
+  "print_format_builder_beta": 0,
+  "print_format_for": "DocType",
+  "print_format_type": "Jinja",
+  "raw_commands": null,
+  "raw_printing": 0,
+  "report": null,
+  "show_section_headings": 0,
+  "standard": "No"
  }
 ]

default_thai_company/hooks.py

@@ -79,6 +79,7 @@ jinja = {
 		"default_thai_company.utils.get_letter_head_company",
 		"default_thai_company.utils.get_company_bank_account",
 		"default_thai_company.utils.get_in_words",
+		"default_thai_company.tax_withholding.get_withholding_certificate",
 	],
 }
 
@@ -100,6 +101,7 @@ fixtures = [
 					"Default Standard Sales Invoice",
 					"Default Standard Tax Invoice/Receipt",
 					"Default Standard Quotation",
+					"Withholding Tax Certificate",
 				],
 			]
 		],

default_thai_company/tax_withholding.py

@@ -11,8 +11,9 @@ from erpnext.accounts.doctype.tax_withholding_category.tax_withholding_category
 	normal_round,
 )
 from frappe import _
+from frappe.contacts.doctype.address.address import get_default_address
 from frappe.modules.utils import sync_customizations_for_doctype
-from frappe.utils import cint, flt
+from frappe.utils import cint, flt, fmt_money, getdate
 
 from default_thai_company.utils import money_in_words
 
@@ -389,3 +390,128 @@ def get_customer_withholding(doc):
 	else:
 		description = _("Withholding tax deducted by customer")
 	return flt(total, precision), description
+
+
+# Withholding tax certificate (หนังสือรับรองการหักภาษี ณ ที่จ่าย, Sec. 50 bis): the income
+# row the payment is reported on, from Tax Withholding Category.income_type (custom field).
+# Rows: 1 = Sec. 40(1), 2 = 40(2), 3 = 40(3), 4a = 40(4)(a), 4b = 40(4)(b) dividends
+# paid from profits taxed at the standard 20% rate (form row 4(b)(1)(1.3)), 5 = payments
+# withheld under Revenue Department orders issued under Sec. 3 tera, 6 = other (specified).
+CERTIFICATE_ROWS = {
+	"Salary and Wages - Sec. 40(1)": "1",
+	"Fees and Commissions - Sec. 40(2)": "2",
+	"Royalties - Sec. 40(3)": "3",
+	"Interest - Sec. 40(4)(a)": "4a",
+	"Dividends - Sec. 40(4)(b)": "4b",
+	"Sec. 3 Tera (Services, Rent, Contract Work etc.)": "5",
+}
+
+THAI_MONTHS = (
+	"มกราคม",
+	"กุมภาพันธ์",
+	"มีนาคม",
+	"เมษายน",
+	"พฤษภาคม",
+	"มิถุนายน",
+	"กรกฎาคม",
+	"สิงหาคม",
+	"กันยายน",
+	"ตุลาคม",
+	"พฤศจิกายน",
+	"ธันวาคม",
+)
+
+
+def pnd_form(row, supplier_type):
+	"""P.N.D. return the certificate row is filed on, as numbered on the form:
+	1 = ภ.ง.ด.1ก, 2 = ภ.ง.ด.2, 3 = ภ.ง.ด.3, 53 = ภ.ง.ด.53.
+
+	Juristic payees (Company; Partnership, taken as registered) file on
+	ภ.ง.ด.53 whatever the income; individuals by income type: salary on
+	ภ.ง.ด.1ก, Sec. 40(3)/(4) on ภ.ง.ด.2, the rest on ภ.ง.ด.3.
+	"""
+	if supplier_type != "Individual":
+		return "53"
+	if row == "1":
+		return "1"
+	if row in ("3", "4a", "4b"):
+		return "2"
+	return "3"
+
+
+def one_line_address(address_name):
+	"""Address in the order of the Thailand Address Template, on one line."""
+	if not address_name:
+		return None
+	address = frappe.get_cached_doc("Address", address_name)
+	parts = [
+		address.address_line1,
+		address.address_line2,
+		address.county,
+		address.city,
+		address.state,
+		address.pincode,
+	]
+	if address.country and address.country != "Thailand":
+		parts.append(address.country)
+	return " ".join(part.strip() for part in parts if part and part.strip())
+
+
+def tax_id_digits(tax_id):
+	"""The 13 digits of a Thai tax ID for the form's boxes, or None when it is not one."""
+	digits = "".join(ch for ch in (tax_id or "") if ch.isdigit())
+	return digits if len(digits) == 13 else None
+
+
+def get_withholding_certificate(doc):
+	"""Certificate data for a Purchase Invoice with Apply Tax Withholding Amount.
+
+	Amounts are in company currency; the form is Thai, so dates are Buddhist Era
+	and the tax in words is Thai whatever the print language.
+	"""
+	company = frappe.get_cached_doc("Company", doc.company)
+	currency = erpnext.get_company_currency(doc.company)
+	precision = doc.precision("base_grand_total")
+
+	category = (
+		frappe.get_cached_doc("Tax Withholding Category", doc.tax_withholding_category)
+		if doc.tax_withholding_category
+		else None
+	)
+	row = CERTIFICATE_ROWS.get(category.income_type if category else None, "6")
+	supplier_type = frappe.get_cached_value("Supplier", doc.supplier, "supplier_type")
+
+	amount = flt(doc.base_tax_withholding_net_total, precision)
+	tax = flt(
+		sum(abs(flt(t.base_tax_amount)) for t in doc.get("taxes") if cint(t.is_tax_withholding_account)),
+		precision,
+	)
+	posting_date = getdate(doc.posting_date)
+
+	return frappe._dict(
+		payer=frappe._dict(
+			name=company.company_name,
+			tax_id=company.tax_id,
+			tax_id_digits=tax_id_digits(company.tax_id),
+			address=one_line_address(get_default_address("Company", doc.company)),
+		),
+		payee=frappe._dict(
+			name=doc.supplier_name,
+			tax_id=doc.tax_id,
+			tax_id_digits=tax_id_digits(doc.tax_id),
+			address=one_line_address(doc.supplier_address or get_default_address("Supplier", doc.supplier)),
+		),
+		row=row,
+		# row 6 prints what was paid for; translations/th.csv carries the fixture categories
+		row_note=_(category.category_name) if row == "6" and category else None,
+		pnd=pnd_form(row, supplier_type),
+		date=f"{posting_date.day:02d}/{posting_date.month:02d}/{posting_date.year + 543}",
+		amount=fmt_money(amount, precision),
+		tax=fmt_money(tax, precision),
+		tax_in_words=money_in_words(tax, currency, lang="th"),
+		issued=frappe._dict(
+			day=posting_date.day,
+			month=THAI_MONTHS[posting_date.month - 1],
+			year=posting_date.year + 543,
+		),
+	)

default_thai_company/templates/print_formats/withholding_tax_certificate.html

@@ -0,0 +1,87 @@
+{#- หนังสือรับรองการหักภาษี ณ ที่จ่าย (Sec. 50 bis certificate) for a Purchase Invoice.
+
+    The Revenue Department's fillable form (approve_wh3_081156.pdf, A4 = 595 x 842 pt) is the page
+    background; every value sits in the rectangle of the corresponding AcroForm field, given here as
+    the PDF's (x0, y0, x1, y1) with the origin at the bottom-left so the numbers can be checked against
+    the form. Two identical copies are printed: copy 1 goes with the payee's tax return, copy 2 is the
+    payee's record. -#}
+{%- set c = get_withholding_certificate(doc) -%}
+{%- set rows = {
+	"1":  {"date": (327, 533, 403, 546), "pay": (411, 533, 490, 547), "tax": (496, 534, 560, 547)},
+	"2":  {"date": (328, 519, 403, 533), "pay": (410, 520, 489, 534), "tax": (496, 519, 560, 532)},
+	"3":  {"date": (328, 504, 403, 518), "pay": (411, 504, 490, 517), "tax": (496, 504, 560, 517)},
+	"4a": {"date": (328, 490, 403, 505), "pay": (412, 490, 491, 504), "tax": (496, 490, 560, 503)},
+	"4b": {"date": (328, 402, 404, 416), "pay": (410, 403, 489, 417), "tax": (497, 403, 562, 416)},
+	"5":  {"date": (327, 216, 403, 230), "pay": (409, 216, 489, 230), "tax": (496, 215, 561, 230)},
+	"6":  {"date": (327, 199, 403, 213), "pay": (409, 199, 489, 213), "tax": (496, 198, 561, 213)},
+} -%}
+{%- set pnd_boxes = {
+	"1": (209, 603, 222, 615),
+	"2": (395, 602, 407, 615),
+	"3": (471, 602, 484, 615),
+	"53": (395, 584, 407, 597),
+} -%}
+{#- Left edges of the printed 13-digit ID boxes (12 pt wide, grouped 1-4-5-2-1), measured on the
+    form; the AcroForm comb field does not line up with them. -#}
+{%- set id_cells = (375, 393, 405, 417, 429, 447.5, 459.5, 471.5, 483.5, 495.5, 513.5, 525.5, 545) -%}
+
+{%- macro box(rect, text, align="left", size=10) -%}
+<div class="f" style="left: {{ rect[0] }}pt; top: {{ 842 - rect[3] }}pt; width: {{ rect[2] - rect[0] }}pt; height: {{ rect[3] - rect[1] }}pt; line-height: {{ rect[3] - rect[1] }}pt; text-align: {{ align }}; font-size: {{ size }}pt;">{{ text }}</div>
+{%- endmacro -%}
+
+{%- macro tick(rect) -%}
+<div class="tick" style="left: {{ rect[0] }}pt; top: {{ 842 - rect[3] }}pt; width: {{ rect[2] - rect[0] }}pt; height: {{ rect[3] - rect[1] }}pt;"></div>
+{%- endmacro -%}
+
+{%- macro tax_id(rect, party) -%}
+	{%- if party.tax_id_digits -%}
+		{%- for digit in party.tax_id_digits -%}
+			{%- set x = id_cells[loop.index0] -%}
+			{{ box((x, rect[1], x + 12, rect[3]), digit, "center") }}
+		{%- endfor -%}
+	{%- elif party.tax_id -%}
+		{{ box(rect, party.tax_id, "center") }}
+	{%- endif -%}
+{%- endmacro -%}
+
+{%- macro amount_row(key) -%}
+	{{ box(rows[key].date, c.date, "center") }}
+	{{ box(rows[key].pay, c.amount, "right") }}
+	{{ box(rows[key].tax, c.tax, "right") }}
+{%- endmacro -%}
+
+{%- for _ in range(2) -%}
+<div class="wht-page">
+	<img class="wht-form" src="/assets/default_thai_company/images/withholding_tax_certificate.png" alt="">
+
+	{#- Invoice reference in the top-right margin; เล่มที่ / เลขที่ are the certificate book's numbers. -#}
+	{{ box((400, 821, 560, 835), doc.name, "right", 8) }}
+
+	{#- ผู้มีหน้าที่หักภาษี ณ ที่จ่าย: the company -#}
+	{{ tax_id((375, 744, 558, 759), c.payer) }}
+	{{ box((54, 729, 316, 745), c.payer.name) }}
+	{{ box((61, 706, 550, 722), c.payer.address or "", "left", 9) }}
+
+	{#- ผู้ถูกหักภาษี ณ ที่จ่าย: the supplier -#}
+	{{ tax_id((375, 676, 558, 690), c.payee) }}
+	{{ box((53, 658, 315, 671), c.payee.name) }}
+	{{ box((59, 627, 550, 643), c.payee.address or "", "left", 9) }}
+
+	{{ tick(pnd_boxes[c.pnd]) }}
+
+	{%- if c.row == "6" %}
+	{{ box((96, 197, 325, 214), c.row_note or "", "left", 8) }}
+	{%- endif %}
+	{{ amount_row(c.row) }}
+	{{ box((409, 180, 488, 196), c.amount, "right") }}
+	{{ box((496, 180, 560, 196), c.tax, "right") }}
+	{{ box((185, 158, 558, 177), c.tax_in_words) }}
+
+	{#- ผู้จ่ายเงิน (1) หัก ณ ที่จ่าย -#}
+	{{ tick((82, 119, 94, 131)) }}
+
+	{{ box((342, 72, 366, 87), c.issued.day, "center") }}
+	{{ box((364, 71, 428, 87), c.issued.month, "center") }}
+	{{ box((429, 72, 470, 87), c.issued.year, "center") }}
+</div>
+{%- endfor -%}

default_thai_company/tests/test_tax_withholding.py

@@ -12,12 +12,15 @@ from default_thai_company.tax_withholding import (
 	LIABILITY_ACCOUNT,
 	OUTPUT_VAT_ACCOUNT,
 	get_payment_entry,
+	get_withholding_certificate,
 	thai_companies,
 )
 
 COMPANY = "_Test WHT Company"
 ABBR = "_TWC"
 CUSTOMER = "_Test WHT Customer"
+SUPPLIER = "_Test WHT Supplier"
+INDIVIDUAL = "_Test WHT Individual"
 ITEM = "_Test WHT Service"
 FIXTURE = frappe.get_app_path("default_thai_company", "fixtures", "tax_withholding_category.json")
 CUSTOM_DIR = frappe.get_app_path("default_thai_company", "default_thai_company", "custom")
@@ -43,6 +46,7 @@ class TestTaxWithholding(FrappeTestCase):
 				"country": "Thailand",
 				"default_currency": "THB",
 				"chart_of_accounts": "Standard",
+				"tax_id": "0105551234567",
 			}
 		).insert()
 		cls.payable = f"{LIABILITY_ACCOUNT} - {ABBR}"
@@ -70,6 +74,35 @@ class TestTaxWithholding(FrappeTestCase):
 			}
 		).insert()
 
+		supplier_group = frappe.db.get_value("Supplier Group", {"is_group": 0})
+		for name, supplier_type, tax_id in (
+			(SUPPLIER, "Company", "0-1234-56789-01-2"),
+			(INDIVIDUAL, "Individual", "1234567890123"),
+		):
+			frappe.get_doc(
+				{
+					"doctype": "Supplier",
+					"supplier_name": name,
+					"supplier_type": supplier_type,
+					"supplier_group": supplier_group,
+					"tax_id": tax_id,
+				}
+			).insert()
+		frappe.get_doc(
+			{
+				"doctype": "Address",
+				"address_title": SUPPLIER,
+				"address_type": "Billing",
+				"address_line1": "99/9 Moo 5",
+				"address_line2": "Soi Sukhumvit 24",
+				"city": "Khlong Toei",
+				"state": "Bangkok",
+				"pincode": "10110",
+				"country": "Thailand",
+				"links": [{"link_doctype": "Supplier", "link_name": SUPPLIER}],
+			}
+		).insert()
+
 	def make_invoice(self, rate=10000, category=None, inclusive=False):
 		si = frappe.get_doc(
 			{
@@ -122,6 +155,31 @@ class TestTaxWithholding(FrappeTestCase):
 	def withheld(self, pe):
 		return [(t.account_head, t.add_deduct_tax, t.tax_amount) for t in pe.taxes]
 
+	def make_purchase_invoice(self, supplier, category, rate=100000):
+		pi = frappe.get_doc(
+			{
+				"doctype": "Purchase Invoice",
+				"company": COMPANY,
+				"supplier": supplier,
+				"set_posting_time": 1,
+				"posting_date": "2026-09-16",
+				"due_date": "2026-09-16",
+				"apply_tds": 1,
+				"tax_withholding_category": category,
+				"items": [{"item_code": ITEM, "qty": 1, "rate": rate}],
+				"taxes": [
+					{
+						"charge_type": "On Net Total",
+						"account_head": f"{INPUT_VAT_ACCOUNT} - {ABBR}",
+						"rate": 7,
+						"description": "VAT 7%",
+					}
+				],
+			}
+		)
+		pi.set_missing_values()
+		return pi.insert()
+
 	def category_account(self, category, company=COMPANY):
 		return frappe.db.get_value(
 			"Tax Withholding Account",
@@ -331,3 +389,34 @@ class TestTaxWithholding(FrappeTestCase):
 		)
 		self.assertEqual(pe.references[0].allocated_amount, 5350.0)
 		self.assertEqual(self.withheld(pe), [(self.receivable, "Deduct", 150.0)])
+
+	def test_certificate_reports_withholding_on_the_category_row(self):
+		pi = self.make_purchase_invoice(SUPPLIER, "WHT 3% - Professional Fee")
+		self.assertEqual(pi.grand_total, 104000.0)  # 100,000 + 7% VAT - 3% withheld
+
+		c = get_withholding_certificate(pi)
+		self.assertEqual((c.row, c.row_note, c.pnd), ("5", None, "53"))
+		self.assertEqual((c.amount, c.tax, c.tax_in_words), ("100,000.00", "3,000.00", "สามพันบาทถ้วน"))
+		self.assertEqual(
+			(c.date, dict(c.issued)), ("16/09/2569", {"day": 16, "month": "กันยายน", "year": 2569})
+		)
+		self.assertEqual((c.payer.name, c.payer.tax_id_digits), (COMPANY, "0105551234567"))
+		self.assertEqual(
+			(c.payee.name, c.payee.tax_id_digits, c.payee.address),
+			(SUPPLIER, "0123456789012", "99/9 Moo 5 Soi Sukhumvit 24 Khlong Toei Bangkok 10110"),
+		)
+
+	def test_certificate_return_follows_payee_type_and_income(self):
+		c = get_withholding_certificate(
+			self.make_purchase_invoice(INDIVIDUAL, "WHT 15% - Interest (Individual)")
+		)
+		self.assertEqual((c.row, c.pnd, c.tax), ("4a", "2", "15,000.00"))
+		self.assertIsNone(c.payee.address)
+
+		c = get_withholding_certificate(
+			self.make_purchase_invoice(INDIVIDUAL, "WHT 15% - Non-Resident Individual")
+		)
+		self.assertEqual((c.row, c.pnd), ("6", "3"))
+		self.assertEqual(
+			c.row_note, "Sec. 40(2)-(6) income paid to non-resident individuals - Sec. 50(2) (P.N.D.3)"
+		)

default_thai_company/utils.py

@@ -5,14 +5,14 @@ from frappe.contacts.doctype.address.address import get_default_address, render_
 from num2words import num2words
 
 
-def money_in_words(amount, currency):
+def money_in_words(amount, currency, lang=None):
-	"""Amount in words for the active language.
+	"""Amount in words for `lang` (default: the active language).
 
 	frappe.utils.money_in_words renders "<currency> <words> only." in every
 	language; Thai documents write "<words>บาทถ้วน" or "<words>บาท<words>สตางค์".
 	Currencies num2words cannot spell in Thai keep frappe's wording.
 	"""
-	if frappe.local.lang == "th":
+	if (lang or frappe.local.lang) == "th":
 		try:
 			return num2words(amount, lang="th", to="currency", currency=currency)
 		except NotImplementedError: