TXT is a file format that contains the text, organized in rows. Text files opposed binaries that contain data that is not intended for interpretation as a text (encoded sound or image). The text file can contain both formatted and unformatted text. Since the very simple text files, they are frequently used for storing data.
DOT is a template file created by Microsoft Word, a word processing application. The DOT file provides a solution for situations where many similar documents with the same font and layout are required with simple changes between them needed, like names and places for example