DOCX was introduced with Microsoft Word 2007, it's based on open XML and uses ZIP compression for smaller file sizes. The benefit of having open XML is that it is able to be read by applications, platforms and Internet Platforms. However to open it using any Microsoft Word that predated 2007 would require DOCX to be converted into a normal doc format.
DOCX improves file and data management and data recovery. DOCX extends what is possible with the binary files of earlier versions. Any application that supports XML can access and work with data in the new file format. The application does not need to be a Microsoft product it can be any application. Users can also use standard transformations to extract or repurpose the data. In addition, security concerns are drastically reduced because the information is stored in XML, which is essentially plain text. Thus, the data can pass through corporate firewalls without hindrance.
Microsoft Word 2007 Microsoft Word 2008 (MAC) OxygenOffice Professional (Linux) Word 2010
PDF is a file format developed by Adobe Systems for representing documents in a manner that is separate from the original operating system, application or hardware from where it was originally created. A PDF file can be any length, contain any number of fonts and images and is designed to enable the creation and transfer of printer-ready output.
Each PDF file encapsulates a complete description of a 2D document (and, with the advent of Acrobat 3D, embedded 3D documents) that includes the text, fonts, images and 2D vector graphics that compose the document. They do not encode information that is specific to the application software, hardware, or operating system used to create or view the document.