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.
CSS.supports("color", this.pageColors.background) &&
          CSS.supports("color", this.pageColors.foreground)
        )
      ) {
        if (this.pageColors.background || this.pageColors.foreground) {
          console.warn(
            "BaseViewer: Ignoring `pageColors`-option, since the browser doesn't support the values used."
          );
        }
        this.pageColors = null;
      }
    }
    this.defaultRenderingQueue = !options.renderingQueue;
    if (this.defaultRenderingQueue) {
      
      this.renderingQueue = new PDFRenderingQueue();
      this.renderingQueue.setViewer(this);
    } else {
      this.renderingQueue = options.renderingQueue;
    }
    this.scroll = watchScroll(this.container, this._scrollUpdate.bind(this));
    this.presentationModeState = PresentationModeState.UNKNOWN;
    this._onBeforeDraw = this._onAfterDraw = null;
    this._resetView();
    if (this.removePageBorders) {
      this.viewer.classList.add("removePageBorders");
    }
    this.updateContainerHeightCss();
  }
  get pagesCount() {