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 (pagesCount > PagesCountLimit.FORCE_SCROLL_MODE_PAGE) {
      console.warn(
        "Forcing PAGE-scrolling for performance reasons, given the length of the document."
      );
      const mode = (this._scrollMode = ScrollMode.PAGE);
      this.eventBus.dispatch("scrollmodechanged", { source: this, mode });
    }
    this._pagesCapability.promise.then(
      () => {
        this.eventBus.dispatch("pagesloaded", { source: this, pagesCount });
      },
      () => {
        
      }
    );
    this._onBeforeDraw = evt => {
      const pageView = this._pages[evt.pageNumber - 1];
      if (!pageView) {
        return;
      }
      
      
      this.#buffer.push(pageView);
    };
    this.eventBus._on("pagerender", this._onBeforeDraw);
    this._onAfterDraw = evt => {
      if (evt.cssTransform || this._onePageRenderedCapability.settled) {
        return;
      }
      this._onePageRenderedCapability.resolve({ timestamp: evt.timestamp });