diff --git a/README.md b/README.md
index 86a0bfa..a544adf 100644
--- a/README.md
+++ b/README.md
@@ -20,6 +20,17 @@ file overrides the upstream Thai for the standard labels the print formats show.
 print formats embed Sarabun (`public/fonts`, OFL) so PDFs render Thai on servers
 without a Thai system font. Switch a user or the print language to `th` to use it.
 
+### Withholding tax certificate
+
+A Purchase Invoice with *Apply Tax Withholding Amount* gets a **Withholding Tax Certificate**
+button that downloads the Revenue Department's Sec. 50 bis form (หนังสือรับรองการหักภาษี ณ ที่จ่าย,
+two copies) as a PDF: the *Withholding Tax Certificate* print format lays the invoice's data
+over the official form (`public/images`). The row the payment is reported on comes from
+*Type of Income Paid* on the Tax Withholding Category (set for the shipped categories; pick it
+for your own), and the ภ.ง.ด. return is ticked from the Supplier's type: ภ.ง.ด.53 for juristic
+payees, ภ.ง.ด.1ก / 2 / 3 by income type for individuals. เล่มที่ / เลขที่ (certificate book
+numbers) and ลำดับที่ (the line in the return) are left for the accountant.
+
 ### Contributing
 
 This app uses `pre-commit` for code formatting and linting. Please [install pre-commit](https://pre-commit.com/#installation) and enable it for this repository:
diff --git a/default_thai_company/hooks.py b/default_thai_company/hooks.py
index f03d515..8a62ea8 100644
--- a/default_thai_company/hooks.py
+++ b/default_thai_company/hooks.py
@@ -43,7 +43,10 @@ required_apps = ["erpnext"]
 # page_js = {"page" : "public/js/file.js"}
 
 # include js in doctype views
-doctype_js = {"Payment Entry": "public/js/payment_entry.js"}
+doctype_js = {
+	"Payment Entry": "public/js/payment_entry.js",
+	"Purchase Invoice": "public/js/purchase_invoice.js",
+}
 # doctype_list_js = {"doctype" : "public/js/doctype_list.js"}
 # doctype_tree_js = {"doctype" : "public/js/doctype_tree.js"}
 # doctype_calendar_js = {"doctype" : "public/js/doctype_calendar.js"}
diff --git a/default_thai_company/public/js/purchase_invoice.js b/default_thai_company/public/js/purchase_invoice.js
new file mode 100644
index 0000000..565ac2d
--- /dev/null
+++ b/default_thai_company/public/js/purchase_invoice.js
@@ -0,0 +1,36 @@
+frappe.ui.form.on("Purchase Invoice", {
+	refresh(frm) {
+		frm.events.toggle_withholding_certificate(frm);
+	},
+
+	apply_tds(frm) {
+		frm.events.toggle_withholding_certificate(frm);
+	},
+
+	toggle_withholding_certificate(frm) {
+		const label = __("Withholding Tax Certificate");
+		frm.remove_custom_button(label);
+		if (!frm.doc.apply_tds || frm.is_new() || frm.doc.docstatus === 2) return;
+		// The Withholding Tax Certificate print format renders the Revenue Department's
+		// Sec. 50 bis form (fixtures/print_format.json) as a PDF.
+		frm.add_custom_button(label, () => {
+			if (frm.is_dirty()) {
+				frappe.msgprint(__("Please save the document before generating the certificate."));
+				return;
+			}
+			const params = new URLSearchParams({
+				doctype: frm.doctype,
+				name: frm.docname,
+				format: "Withholding Tax Certificate",
+				no_letterhead: 1,
+				_lang: "th",
+			});
+			const w = window.open(
+				frappe.urllib.get_full_url(
+					`/api/method/frappe.utils.print_format.download_pdf?${params}`
+				)
+			);
+			if (!w) frappe.msgprint(__("Please enable pop-ups"));
+		});
+	},
+});
diff --git a/default_thai_company/translations/th.csv b/default_thai_company/translations/th.csv
index c64b81e..8e210ef 100644
--- a/default_thai_company/translations/th.csv
+++ b/default_thai_company/translations/th.csv
@@ -60,6 +60,8 @@ Withholding Tax Payable,ภาษีหัก ณ ที่จ่ายค้า
 Withholding Tax Receivable,ภาษีถูกหัก ณ ที่จ่าย
 Output VAT,ภาษีขาย
 Input VAT,ภาษีซื้อ
+Withholding Tax Certificate,หนังสือรับรองการหักภาษี ณ ที่จ่าย
+Please save the document before generating the certificate.,กรุณาบันทึกเอกสารก่อนออกหนังสือรับรองการหักภาษี ณ ที่จ่าย
 Type of Income Paid,ประเภทเงินได้พึงประเมินที่จ่าย
 Salary and Wages - Sec. 40(1),เงินเดือน ค่าจ้าง ฯลฯ ตามมาตรา 40(1)
 Fees and Commissions - Sec. 40(2),ค่าธรรมเนียม ค่านายหน้า ฯลฯ ตามมาตรา 40(2)