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.
value: false,
    kind: OptionKind.VIEWER + OptionKind.PREFERENCE,
  },
  enablePrintAutoRotate: {
    
    value: true,
    kind: OptionKind.VIEWER + OptionKind.PREFERENCE,
  },
  enableScripting: {
    
    value: typeof PDFJSDev === "undefined" || !PDFJSDev.test("CHROME"),
    kind: OptionKind.VIEWER + OptionKind.PREFERENCE,
  },
  externalLinkRel: {
    
    value: "noopener noreferrer nofollow",
    kind: OptionKind.VIEWER,
  },
  externalLinkTarget: {
    
    value: 0,
    kind: OptionKind.VIEWER + OptionKind.PREFERENCE,
  },
  historyUpdateUrl: {
    
    value: false,
    kind: OptionKind.VIEWER + OptionKind.PREFERENCE,
  },
  ignoreDestinationZoom: {