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,
  },
  imageResourcesPath: {
    
    value: "./images/",
    kind: OptionKind.VIEWER,
  },
  maxCanvasPixels: {
    
    value: 16777216,
    kind: OptionKind.VIEWER,
  },
  pageColorsBackground: {
    
    value: "Canvas",
    kind: OptionKind.VIEWER + OptionKind.PREFERENCE,
  },
  pageColorsForeground: {
    
    value: "CanvasText",
    kind: OptionKind.VIEWER + OptionKind.PREFERENCE,
  },
  pdfBugEnabled: {
    
    value: typeof PDFJSDev === "undefined" || !PDFJSDev.test("PRODUCTION"),
    kind: OptionKind.VIEWER + OptionKind.PREFERENCE,
  },
  printResolution: {