mozilla/pdf.js · error · Error

doc.path is read-only

Error message

doc.path is read-only

What it means

`Doc.path` returns the device-independent path of the open document; PDF.js returns `""` because documents loaded in a browser have no filesystem path. It is read-only per the Acrobat spec — the path is a factual attribute of how the doc was opened, not something a script can change. The throwing setter enforces that contract.

Source

Thrown at src/scripting_api/doc.js:591

    }
    this._send({ command: "page-num", value });
    this._pageNum = value;
  }

  get pageWindowRect() {
    return [0, 0, 0, 0];
  }

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

  get path() {
    return "";
  }

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

  get permStatusReady() {
    return true;
  }

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

  get producer() {
    return this._producer;
  }

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

View on GitHub (pinned to 5903d58d58)

Solutions

  1. Remove the assignment; read `doc.path` (returns `""` in PDF.js) or `doc.URL` for the source location.
  2. Manage save paths at the host integration layer rather than inside the document script.
  3. Wrap script execution in try/catch to tolerate legacy save code.

Example fix

// before
doc.path = '/tmp/saved.pdf';

// after
var src = doc.URL; // read-only source; doc.path returns '' in browser
Defensive patterns

Strategy: validation

Validate before calling

const READ_ONLY_DOC_PROPS = new Set(['path','URL' /* ... */]);
function assertsNoReadOnlyWrite(scriptSrc) {
  for (const p of READ_ONLY_DOC_PROPS) {
    if (new RegExp(`\\bdoc\\.${p}\\s*=[^=]`).test(scriptSrc)) {
      throw new Error(`Script writes read-only property doc.${p}`);
    }
  }
}
assertsNoReadOnlyWrite(myScript);

Type guard

function isReadOnlyDocProp(doc, prop) {
  const desc = Object.getOwnPropertyDescriptor(Object.getPrototypeOf(doc), prop)
    || Object.getOwnPropertyDescriptor(doc, prop);
  return !!desc && !!desc.get && !desc.set;
}
isReadOnlyDocProp(doc, 'path'); // true

Try / catch

try {
  doc.path = '/tmp/saved.pdf';
} catch (e) {
  if (/\\bpath is read-only/.test(e.message)) console.warn(e.message);
  else throw e;
}

Prevention

When it happens

Trigger: A script writes `doc.path = '/some/file.pdf';`, typically to record or fake a save location. The setter throws immediately.

Common situations: Save/export scripts ported from desktop Acrobat; scripts trying to derive a working directory from `doc.path`; code that assumes a writable path field.

Related errors

AI-assisted analysis of mozilla/pdf.js@5903d58d58 (2026-08-13). Data as JSON: /api/errors/eb451639875a7754. Report an issue: GitHub.