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.
if (!AppOptions.get("pdfBugEnabled")) {
      return;
    }
    const hash = document.location.hash.substring(1);
    if (!hash) {
      return;
    }
    const { mainContainer, viewerContainer } = this.appConfig,
      params = parseQueryString(hash);
    if (params.get("disableworker") === "true") {
      try {
        await loadFakeWorker();
      } catch (ex) {
        console.error(`_parseHashParameters: "${ex.message}".`);
      }
    }
    if (params.has("disablerange")) {
      AppOptions.set("disableRange", params.get("disablerange") === "true");
    }
    if (params.has("disablestream")) {
      AppOptions.set("disableStream", params.get("disablestream") === "true");
    }