A C++ library to access PDF-files at the object level.
License: GNU Lesser GPL

Functionality like "pdfselect" or even an "Acrobat Pro"-clone can then be implemented on top of it - the PDF-Reference will be your friend :-)

Have a look at CurrentStatus.

This project also includes two independently usable C libraries:

• g4coder - a G3/G4 Fax En-/Decoder
• lzwcoder - a (TIFF) LZW En-/Decoder

The wiki contains some notes.

Another somehow related project is libfontembed, which aims to encapsulate all the details required to embed TTF or OTF(CFF) (for now; also subsetting only for TTF) into PDF files (some PS support is already there). It is released under the MIT License and available via the Openprinting/Linuxfoundation bazaar repository, as its currenty primary user is texttopdf from cups-filters: View Bazaar Repository