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.
this._pages.push(pageView);
        }
        
        
        
        const firstPageView = this._pages[0];
        if (firstPageView) {
          firstPageView.setPdfPage(firstPdfPage);
          this.linkService.cachePageRef(1, firstPdfPage.ref);
        }
        if (this._scrollMode === ScrollMode.PAGE) {
          
          this.#ensurePageViewVisible();
        } else if (this._spreadMode !== SpreadMode.NONE) {
          this._updateSpreadMode();
        }
        
        
        
        this.#onePageRenderedOrForceFetch().then(async () => {
          if (this.findController) {
            this.findController.setDocument(pdfDocument); 
          }
          if (this._scriptingManager) {
            this._scriptingManager.setDocument(pdfDocument); 
          }
          
          
          if (
            pdfDocument.loadingParams.disableAutoFetch ||