azw4 .azw4 file extension is a file format developed by Amazon and is used by applications specifically designed for e-readers. It is mainly found on Kindle e-reader devices, a Kindle software is also available for desktops that allows interpretation and reading of azw4 files. It is used to read e-books normally purchased online. The greatest benefit that comes with using azw4 is that text does not have to stay static, so files transferred from a device with a larger screen to one with a smaller screen are adjusted and one does not have to zoom in order to read.
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.