VLC Media Player - VLC is a free and open source cross-platform multimedia player and framework.
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
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.
online2pdf - This Online PDF Converter can convert all your files to PDF but also compress and merge PDF files! Word, Excel, PowerPoint, images and any other kind of document can be easily converted to PDF on Online2PDF.