We could use:
https://github.com/mozilla/pdf.js/blob/c3d08580627471432a6ad0b2fdb948df64126afa/src/display/api.js#L929

and look at bit 4.

The following pdf:
https://orimi.com/pdf-test.pdf
is not editable in neither Acrobat nor Edge nor Foxit and nor Okular.
workerSrc: {
    
    value:
      typeof PDFJSDev === "undefined" || !PDFJSDev.test("PRODUCTION")
        ? "../src/worker_loader.js"
        : "../build/pdf.worker.js",
    kind: OptionKind.WORKER,
  },
};
if (
  typeof PDFJSDev === "undefined" ||
  PDFJSDev.test("!PRODUCTION || GENERIC")
) {
  defaultOptions.defaultUrl = {
    
    value: "compressed.tracemonkey-pldi-09.pdf",
    kind: OptionKind.VIEWER,
  };
  defaultOptions.disablePreferences = {
    
    value: typeof PDFJSDev !== "undefined" && PDFJSDev.test("TESTING"),
    kind: OptionKind.VIEWER,
  };
  defaultOptions.locale = {
    
    value: navigator.language || "en-US",
    kind: OptionKind.VIEWER,
  };
  defaultOptions.renderer = {