docx
DOCX is a well-known format for Microsoft Word documents.
Introduced from 2007 with the release of Microsoft Office 2007, the structure of this new Document format was changed from plain binary to a combination of XML and binary files.
Docx files can be opened with Word 2007 and lateral versions but not with the earlier versions of MS Word which support DOC file extensions.
txt
A file with .TXT extension represents a text document that contains plain text in the form of lines.
Paragraphs in a text document are recognized by carriage returns and are used for better arrangement of file contents.
A standard text document can be opened in any text editor or word processing application on different operating systems.
All the text contained in such a file is in human-readable format and represented by sequence of characters.