mozilla/pdf.js · error · Error

app.fromPDFConverters is read-only

Error message

app.fromPDFConverters is read-only

What it means

app.fromPDFConverters is a stub returning an empty array (PDF.js has no registered PDF import converters). Per the Acrobat JS API the list is viewer-managed, so the setter throws. Assignment is rejected unconditionally.

Source

Thrown at src/scripting_api/app.js:238

  set focusRect(val) {
    /* TODO or not */
    this._focusRect = val;
  }

  get formsVersion() {
    return FORMS_VERSION;
  }

  set formsVersion(_) {
    throw new Error("app.formsVersion is read-only");
  }

  get fromPDFConverters() {
    return [];
  }

  set fromPDFConverters(_) {
    throw new Error("app.fromPDFConverters is read-only");
  }

  get fs() {
    return (this._fs ??= new Proxy(
      new FullScreen({ send: this._send }),
      this._proxyHandler
    ));
  }

  set fs(_) {
    throw new Error("app.fs is read-only");
  }

  get language() {
    return this._language;
  }

  set language(_) {

View on GitHub (pinned to 5903d58d58)

Solutions

1. Do not assign to app.fromPDFConverters; treat it as a viewer-provided (here empty) list.
2. Implement any conversion outside the scripting API if needed.
3. Read the property to confirm no converters are available before falling back.

Example fix

// before
app.fromPDFConverters = [myConverter];
// after
const converters = app.fromPDFConverters; // always [] in pdf.js

// fromPDFConverters always returns [] in pdf.js; just read it.
const converters = Array.isArray(app.fromPDFConverters) ? app.fromPDFConverters : [];

const isEmptyViewerList = (v) => Array.isArray(v) && v.length === 0;

try { /* code that may assign app.fromPDFConverters */ }
catch (e) { if (!/fromPDFConverters is read-only/.test(e.message)) throw e; }

When it happens

Trigger: PDF JavaScript or caller executes app.fromPDFConverters = [...]; the setter at src/scripting_api/app.js:238 throws regardless of argument.

Common situations: Scripts that try to register custom converter plugins; confusion with an extensible plugin registry.

Related errors

• app.monitors is read-only
• app.numPlugins is read-only
• app.plugins is read-only
• app.activeDocs is read-only
• app.constants is read-only

AI-assisted analysis of mozilla/pdf.js@5903d58d58 (2026-08-13). Data as JSON: /api/errors/b9803627e2aa60e4. Report an issue: GitHub.