The best thing to do would be to try to obtain the source documents from which these PDFs are produced, and re-export to PDF using minimal margins and your screen size and page size. Often you cannot do this, however,
Failing that, I highly recommend using using some of the tools you'll find (or find discussion of) around here, particularly
sopdf (my favorite for text-based PDFs) and
pdflrf (which I prefer for scanned PDFs).
There are some others too, like PDFRead, you can try too, but the two above are my favorite.