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.
eventBus,
      });
      pdfLinkService.setHistory(this.pdfHistory);
    }
    if (!this.supportsIntegratedFind) {
      this.findBar = new PDFFindBar(appConfig.findBar, eventBus, this.l10n);
    }
    this.pdfDocumentProperties = new PDFDocumentProperties(
      appConfig.documentProperties,
      this.overlayManager,
      eventBus,
      this.l10n,
       () => {
        return this._docFilename;
      }
    );
    this.pdfCursorTools = new PDFCursorTools({
      container,
      eventBus,
      cursorToolOnLoad: AppOptions.get("cursorToolOnLoad"),
    });
    this.toolbar = new Toolbar(appConfig.toolbar, eventBus, this.l10n);
    this.secondaryToolbar = new SecondaryToolbar(
      appConfig.secondaryToolbar,
      eventBus
    );
    if (this.supportsFullscreen) {
      this.pdfPresentationMode = new PDFPresentationMode({
        container,
        pdfViewer: this.pdfViewer,