xls The .xls filename extension is a native binary file format associated with the closed source spreadsheet application Microsoft Office Excel. First introduced in 1987 with the release of Excel 2.x, the file format acts as the container for storing spreadsheet data such as work sheets, charts, and macros. Prior to Microsoft Office Excel 2007, the xls binary format was the default standard for the Microsoft Office Excel until the later adoption of the Open Document standard .xlsx. Documents to be saved in the .xls format are saved as Excel 97, 2003 documents.
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.