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.
pageIndexSet.add(pageNumber - 1);
      }
      
      const spread = document.createElement("div");
      spread.className = "spread";
      if (this.isInPresentationMode) {
        const dummyPage = document.createElement("div");
        dummyPage.className = "dummyPage";
        spread.append(dummyPage);
      }
      for (const i of pageIndexSet) {
        const pageView = this._pages[i];
        if (!pageView) {
          continue;
        }
        spread.append(pageView.div);
        state.pages.push(pageView);
      }
      viewer.append(spread);
    }
    state.scrollDown = pageNumber >= state.previousPageNumber;
    state.previousPageNumber = pageNumber;
  }
  _scrollUpdate() {
    if (this.pagesCount === 0) {
      return;
    }
    this.update();
  }
  #scrollIntoView(pageView, pageSpot = null) {