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.
evt.dataTransfer.dropEffect =
        evt.dataTransfer.effectAllowed === "copy" ? "copy" : "move";
    });
    appConfig.mainContainer.addEventListener("drop", function (evt) {
      evt.preventDefault();
      const { files } = evt.dataTransfer;
      if (!files || files.length === 0) {
        return;
      }
      eventBus.dispatch("fileinputchange", {
        source: this,
        fileInput: evt.dataTransfer,
      });
    });
  }
  if (!PDFViewerApplication.supportsDocumentFonts) {
    AppOptions.set("disableFontFace", true);
    PDFViewerApplication.l10n.get("web_fonts_disabled").then(msg => {
      console.warn(msg);
    });
  }
  if (!PDFViewerApplication.supportsPrinting) {
    appConfig.toolbar.print.classList.add("hidden");
    appConfig.secondaryToolbar.printButton.classList.add("hidden");
  }
  if (!PDFViewerApplication.supportsFullscreen) {
    appConfig.toolbar.presentationModeButton.classList.add("hidden");
    appConfig.secondaryToolbar.presentationModeButton.classList.add("hidden");
  }
  if (PDFViewerApplication.supportsIntegratedFind) {