Can QuickPDF report on 'hidden' text?

I have two near-identical customer PDFs.

When I look at them in Okular or Sumatra, I see a table and in one cell is 'S'. However, using QuickPDF to extract the text I find that in one PDF's cell the text is 'S' as shown, but in the other PDF the text is actually 'SUPER'.

The reason the 'UPER' part isn't visible is because it is underneath the following cells in the row. (I also checked in case it was white text on white, but no, all the text in these PDFs is black.)

So, is there a QuickPDF function that could tell me if some text is not actually visible? Or is there a function that can let me say that when I extract text I only want visible text?

PS I can't give you the PDFs to look at. One was generated using PDFLib 7.0.1p1 and the other with PDFLib 9.0.3p3.

Thanks.