pdfsig does not detect that the document has a modified page
Regarding the attached file, Adobe Reader DC says that the page has been modified after signing (which is technically false, but well, some people think that Adobe Reader DC is the gold standard regarding PDF). However, pdfsig does not complain about anything. I am afraid that, because of this discrepancy, somebody might construct a truly modified pdf document that passes pdfsig validation.
I.e.: could you please look at the file TestSign.pdf and figure out why Adobe Reader DC complains about the modified page? If the reason for the complaint is legitimate, pdfsig must complain, too.