Note: this is not against you, because (unless you created the document) you can not do much about it.
The scenario shows a serious lack of understanding of the way digital signatures work. A digital signature is essentially a seal around the document; it can confirm that the signer was actually who he claims to be, and that at the time the signature was assigned, the document was exactly like that.
A digital signature always concerns the whole document. And that's the reason why the document must be saved when it is applied. Any subsequent modifications "invalidate" (which is not really the correct term; it would be better to say they make the signature no longer current) the signature, and applying another digital signature "invalidates" the previous one(s).
I can imagine what the intention of signing every page is; it is the equivalent of adding initials or a signature to confirm that one has looked at the page. In the digital world, that would be an "electronic" signature, described very simply as a stamp (in fact, that's what it is technically spoken in Acrobat; you create an image of your wet signature, and turn it into a stamp, and apply it). Now, after stamping all the pages, you apply a digital signature, and that confirms the stamps as well.
But, as said, you did not set up the document, and therefore, you can not do much about it other than grumble.
Hope this can help.
Max Wyss.