I downloaded a PDF book. It looks like someone added a footer to each page of the original, and that pushed the content up on each page so that the first half inch of each page’s isn’t visible.

I fixed the PDF by:

• Downloading and installing the brew (homebrew) package manager. (I use a Mac.)
• Running “brew install ghostscript”.

• Running

  gs -sOutputFile=output.pdf -sDEVICE=pdfwrite -sPAPERSIZE=a4 -dCompatibilityLevel=1.4 -dNOPAUSE -dBATCH -dPDFFitPage input.pdf

See http://ghostscript.com/doc/7.07/Use.htm#Known_paper_sizes

Or use “-dDEVICEWIDTHPOINTS=w -dDEVICEHEIGHTPOINTS=h” where w is width and h is height, in 1/72” (points).

OS X Preview can show you the page size via Tools > Show Inspector. Then multiply the dimensions in inches by 72 and round up to an integer.