pdf The .pdf file format extension was developed by Adobe systems in 1993 as a means of presenting documents in a consistent manner across different platforms, hardware, operating systems, and applications. The format was not released as an open source document format until 2008, though minimal proprietary technologies still controlled by Adobe Systems exist in the format. Every .pdf document carries with it the necessary meta information required to properly reconstruct the text, fonts, and graphics used to produce the document. This ensures that documents will be viewed in exactly the same way the author intended regardless of the device used to open the document. From conception to date, Adobe Systems has continued to support the format adding features with every iteration of the standard including hardened algorithms for document encryption and privacy. Today, many freely available readers exist allowing you to open and view .pdf documents and create or convert other file formats such as .jpeg and .doc into .pdf documents.
ppm The .ppm file extension is used for Portable PixMap format files and is intended to be an intermediate format that can be used in the development and conversion of other file formats. This format was specifically designed so that it could easily be exchanged between various platforms. It is very simple but not very storage efficient. Before the PPM format was introduced, Jef Poskanzer invented the PBM format in the year 1980 for transmission of monochrome bitmaps as ASCII text in email messages. He also developed a tool library for easy conversion of the PBM files to other graphical formats and vice versa. This library was called Pbmplus and was released in 1988. Later Poskanzer developed the PPM format along with the PGM format and the requisite tools that were added to Pbmplus.