VersyPDF is a pure C library for create / modify PDF documents on the fly.

VersyPDF is a high-quality, industry-strength PDF library meeting requirements of the most demanding and diverse applications. Using VersyPDF you can write stand-alone, cross-platform and reliable commercial applications that can read, write, and edit PDF documents.

Features:
Read/write a PDF document from/to memory buffer or a file on a disk.
Create new text, vector art and images.
Quick image embedding for TIFF, JPEG, PNG, and BMP.
Support for Type1 and TrueType font embedding for accurate text reproduction.
Support for Unicode text and standard PDF encodings.
Dynamic font subsetting resulting in smaller files.
Full control over text positioning and character spacing.
Support for all PDF color spaces and advanced pre-press options.
Full control over content positioning and all graphical attributes available in PDF.
Reuse of resources such as images, fonts and color spaces through object sharing resulting in smaller and more efficient documents.
Support for explicit and named destinations. Named destinations allow for changes to the document that will not invalidate existing bookmarks.
Extensive bookmark creation and editing API.
Work with threads.
Apply security to new documents.
Linearization (Fast Web View)
Compression of the output PDF documents
Insert or append new content to existing pages.
Rotate pages.
JBIG2, CCITT Fax, Flate/PNG, JPEG/DCT compression.
Support for Standard PDF security handler (40 and 128 bit encryption)
Unused object removal. This option can help you create smaller files.
Fill PDF Forms
Read PDF form fields values
Create new form fields
Split pages
Merge and append pages
Digital Signature support
Lot of the actions support
Lot of the annotations support
EMF images parsing

The VersyPDF Library do not require any third-party software for creating or modifying PDF files.