mendix · samuelreichert · Jun 12, 2026 · Jun 12, 2026 · Jun 12, 2026
@@ -0,0 +1,63 @@
+# Bug: PDF Form Checkboxes Not Displaying Checked State
+
+**Widget:** Document Viewer v1.2.0
+**Mendix version:** 10.24.9
+**Status:** Fixed
+
+---
+
+## Symptom
+
+A W9 PDF generated via .NET has a checked checkbox in Section 3.a ("C corporation"). When opened directly in a browser (Chrome, Firefox native viewer), the checkbox renders correctly as checked. When displayed in the Document Viewer widget, the checkbox appears unchecked.
+
+---
+
+## Root Cause
+
+The checkmark is drawn by a PDF Form XObject using the `/ZaDb` (ZapfDingbats) standard font with glyph `0x34`. PDF.js substitutes standard fonts with bundled Foxit equivalents, fetching them from `standardFontDataUrl`.
+
+`PDFViewer.tsx` configured this as a relative URL:
+
+```ts
+const options = {
+    cMapUrl: "/widgets/com/mendix/shared/pdfjs/cmaps/",
+    standardFontDataUrl: "/widgets/com/mendix/shared/pdfjs/standard_fonts/"
+};
+```
+
+The PDF.js worker is loaded from `//unpkg.com/pdfjs-dist@.../pdf.worker.min.mjs` — a cross-origin URL. A worker loaded from a different origin has no document base URL, so `fetch()` cannot resolve relative paths. The worker throws:
+
+```
+TypeError: Failed to execute 'fetch' on 'WorkerGlobalScope':
+Failed to parse URL from /widgets/com/mendix/shared/pdfjs/standard_fonts/FoxitDingbats.pfb
+```
+
+Font load silently fails → ZapfDingbats not available → checkmark glyph renders as blank rectangle.
+
+The browser's native PDF viewer is unaffected because it handles font resolution internally without a web worker.
+
+---
+
+## Fix
+
+**File:** `packages/pluggableWidgets/document-viewer-web/src/components/PDFViewer.tsx`
+
+```diff
++const origin = window.location.origin;
+ const options = {
+-    cMapUrl: "/widgets/com/mendix/shared/pdfjs/cmaps/",
+-    standardFontDataUrl: "/widgets/com/mendix/shared/pdfjs/standard_fonts/"
++    cMapUrl: `${origin}/widgets/com/mendix/shared/pdfjs/cmaps/`,
++    standardFontDataUrl: `${origin}/widgets/com/mendix/shared/pdfjs/standard_fonts/`
+ };
+```
+
+`window.location.origin` is the Mendix app origin (e.g. `https://myapp.mendixcloud.com`). The worker can fetch absolute URLs regardless of where it was loaded from.
+
+---
+
+## Verification
+
+1. Load customer W9 PDF — Section 3.a "C corporation" checkbox shows as checked ✓
+2. Build: `pnpm --filter @mendix/document-viewer-web run build`
+3. Network tab shows absolute URL `http://<host>/widgets/.../FoxitDingbats.pfb` with 200 response (or request goes to worker — confirmed via console, no more `loadFont` warning)
@@ -0,0 +1,2 @@
+schema: spec-driven
+created: 2026-06-11
@@ -0,0 +1,34 @@
+## Context
+
+Document Viewer v1.2.0 uses `react-pdf` to render PDFs via PDF.js. The `options` object passed to the `<Document>` component includes `cMapUrl` and `standardFontDataUrl` as relative paths. PDF.js passes these to the worker thread for font/cmap fetching. When the worker is loaded from a cross-origin URL (the default is unpkg CDN: `//unpkg.com/pdfjs-dist@.../pdf.worker.min.mjs`), the worker's `fetch()` cannot resolve relative URLs — it has no document origin to resolve against — causing a `TypeError: Failed to parse URL` and silent font load failure.
+
+The customer's W9 PDF draws a checkmark using the ZapfDingbats standard font (glyph `0x34`) via a Form XObject. Without the font, PDF.js renders a blank rectangle.
+
+## Goals / Non-Goals
+
+**Goals:**
+
+- Fix standard font and cmap fetching when the PDF.js worker is cross-origin
+- No new XML properties, no API surface changes, no dependency updates
+
+**Non-Goals:**
+
+- Changing how the worker URL is configured
+- Supporting self-hosted worker deployments (already supported via `pdfjsWorkerUrl` prop)
+
+## Decisions
+
+### Use `window.location.origin` to make resource URLs absolute
+
+Prepend `window.location.origin` to both `cMapUrl` and `standardFontDataUrl` at module evaluation time.
+
+**Rationale:** The worker needs absolute URLs. `window.location.origin` is always the Mendix app origin — correct for all deployment environments. Evaluated at module load (not per-render), so no React re-render cost.
+
+**Alternative considered:** Move `options` inside the component and use `useMemo`. Rejected — no reactive dependencies, module-scope evaluation is simpler and equivalent.
+
+**Alternative considered:** Set `useWorkerFetch: false` to force main-thread font loading. Rejected — works around the symptom, not the cause; disabling worker fetch has broader performance implications.
+
+## Risks / Trade-offs
+
+- `window.location.origin` is not available in SSR/test environments. Tests currently stub this or don't exercise PDF rendering — no impact. If server-side rendering is ever added, this will need to be guarded.
+- If the Mendix app is served from a subpath (e.g. `/app/`), `origin` alone is correct — fonts live under `/widgets/`, not the subpath.
@@ -0,0 +1,25 @@
+## Why
+
+PDFs containing glyphs from ZapfDingbats (a PDF standard font) — such as checkmarks generated by .NET PDF libraries — render blank in Document Viewer. The checkmark is drawn via a Form XObject using the ZapfDingbats font, which PDF.js must fetch from `standardFontDataUrl`. The URL was relative, causing the PDF.js worker (loaded from unpkg CDN, a different origin) to fail parsing it as an absolute URL.
+
+## What Changes
+
+- `standardFontDataUrl` and `cMapUrl` in `PDFViewer.tsx` are prefixed with `window.location.origin` to produce absolute URLs, allowing the worker to fetch font resources regardless of where it was loaded from.
+
+## Capabilities
+
+### New Capabilities
+
+- `pdf-form-rendering`: Correct visual rendering of standard-font glyphs (ZapfDingbats checkmarks, Symbol characters) in PDFs rendered by the Document Viewer widget
+
+### Modified Capabilities
+
+<!-- none -->
+
+## Impact
+
+- **File**: `packages/pluggableWidgets/document-viewer-web/src/components/PDFViewer.tsx`
+- **Behavior**: ZapfDingbats and other standard font glyphs now render correctly when PDF.js worker is loaded from a cross-origin URL (e.g. unpkg CDN)
+- **No API or XML changes**
+- **No dependency version changes**
+- **Affected widget**: `@mendix/document-viewer-web` v1.2.0+
@@ -0,0 +1,21 @@
+## ADDED Requirements
+
+### Requirement: Standard font glyphs render correctly in PDFs
+
+The Document Viewer SHALL correctly render PDF glyphs that depend on PDF standard fonts (ZapfDingbats, Symbol, etc.) by fetching font resources using absolute URLs resolvable by the PDF.js worker.
+
+#### Scenario: ZapfDingbats checkmark renders in cross-origin worker context
+
+- **WHEN** a PDF contains a glyph drawn from the ZapfDingbats standard font (e.g. a checkmark drawn via a Form XObject)
+- **AND** the PDF.js worker is loaded from a cross-origin URL (e.g. unpkg CDN)
+- **THEN** the glyph SHALL render visibly on the canvas
+
+#### Scenario: Font fetch uses absolute URL
+
+- **WHEN** PDF.js requests a standard font file from the worker thread
+- **THEN** the request URL SHALL be an absolute URL including the application origin (e.g. `https://example.com/widgets/.../FoxitDingbats.pfb`)
+
+#### Scenario: PDFs without standard fonts are unaffected
+
+- **WHEN** a PDF contains no glyphs requiring standard font substitution
+- **THEN** rendering SHALL be identical to previous behavior
@@ -0,0 +1,10 @@
+## 1. Implementation
+
+- [x] 1.1 Prepend `window.location.origin` to `cMapUrl` and `standardFontDataUrl` in `packages/pluggableWidgets/document-viewer-web/src/components/PDFViewer.tsx`
+
+## 2. Verification
+
+- [x] 2.1 Run unit tests: `cd packages/pluggableWidgets/document-viewer-web && pnpm run test`
+- [x] 2.2 Build widget: `pnpm --filter @mendix/document-viewer-web run build`
+- [x] 2.3 Verify customer W9 PDF shows Section 3.a checkbox as checked in Document Viewer
+- [x] 2.4 Verify a PDF without AcroForms renders correctly (no regression)
@@ -10,6 +10,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 - We changed the internal structure of the widget
 
+### Fixed
+
+- We fixed an issue where PDF standard fonts (e.g. ZapfDingbats) failed to load when the PDF.js worker was served from a cross-origin URL, causing glyphs such as checkmarks to render as blank rectangles.
+
 ## [1.2.0] - 2025-10-29
 
 ### Added

@@ -4,12 +4,14 @@
 import "react-pdf/dist/Page/TextLayer.css";
 import { downloadFile } from "../utils/helpers";
 import { useZoomScale } from "../utils/useZoomScale";
 import BaseViewer from "./BaseViewer";
 import { DocRendererElement, DocumentRendererProps, DocumentStatus } from "./documentRenderer";
 import { If } from "@mendix/widget-plugin-component-kit/If";
+
+const origin = window.location.origin;
 const options = {
-    cMapUrl: "/widgets/com/mendix/shared/pdfjs/cmaps/",
-    standardFontDataUrl: "/widgets/com/mendix/shared/pdfjs/standard_fonts"
+    cMapUrl: `${origin}/widgets/com/mendix/shared/pdfjs/cmaps/`,
+    standardFontDataUrl: `${origin}/widgets/com/mendix/shared/pdfjs/standard_fonts/`
 };
 
 const PDFViewer: DocRendererElement = (props: DocumentRendererProps) => {