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.
for (const { id, y, percent, widthPercent } of views) {
          if (percent === 0 || widthPercent < 100) {
            continue;
          }
          let yArray = pageLayout.get(y);
          if (!yArray) {
            pageLayout.set(y, (yArray ||= []));
          }
          yArray.push(id);
        }
        
        for (const yArray of pageLayout.values()) {
          const currentIndex = yArray.indexOf(currentPageNumber);
          if (currentIndex === -1) {
            continue;
          }
          const numPages = yArray.length;
          if (numPages === 1) {
            break;
          }
          
          if (previous) {
            for (let i = currentIndex - 1, ii = 0; i >= ii; i--) {
              const currentId = yArray[i],
                expectedId = yArray[i + 1] - 1;
              if (currentId < expectedId) {
                return currentPageNumber - expectedId;
              }
            }