PDF Clown - PDF Clown is an open-source general-purpose library for manipulating PDF documents through multiple abstraction layers, rigorously adhering to PDF 1.7 Specification
VLC Media Player - VLC is a free and open source cross-platform multimedia player and framework.
ABCpdf.NET - ABCpdf.NET is a high-profile and powerful PDF Library that delivers the best experience possible for everyone.
AIMP - AIMP : Free Audio Player : Официальный сайт программы
Document .Net - Gives you API to do everything with a document in PDF, DOCX, DOC, RTF, HTML and Text formats.
foobar2000 - An advanced freeware audio player for the Windows platform.