Test PDF parser with different PDF structures

I have an application that signs PDF files with digital signature. As the PDF format is quite diverse in its structure, i want to test this code with as many different PDF structures as i can find. I once found a page where there was a set of PDF files with different structures (AcroForm inlined in root, Aroform indirectly referenced, etc.) but i cant seem to find it anymore. Does someone know this page or any other resource that has different PDF structure samples, so that i could test if my application can handle the different ways a PDF is constructed?