DOCX is a file extension originally used for the text documents natively generated by Microsoft Office Word 2007 and later. It has later grown to be frequently used for business and academic papers.
Even though it resembles the DOC format, the way DOCX stores document data is as a collection of distinct files and folders compressed using ZIP method.
DOCX can be accessed by a wide range of applications, considering all the word processors that were updated recently support the format.
There are also some DOCX viewers that will allow users to modify the file's contents, but this functionality is encountered only in some dedicated apps.