qpdf

qpdf is a command-line tool and library that performs structural transformations on PDF files without touching the visible content. It is used to repair damaged files, remove or add encryption and passwords, merge and split pages, prepare files for fast web view and inspect the object structure of a file. It is especially handy in scripts that process large numbers of reports and drawings, and as a helper when another program fails to open a file. Limitation: there is no GUI, and it does not convert formats, compress images or run OCR.