TXT is one of the simplest and longest existing text file formats. The full name of the format is Plain Text File, and the developer is unknown. Text files of this format are very small, and therefore have become very widespread. A TXT file contains text data organized as strings. As a rule, this is a standard text document without formatting. This format is universal, it is available to work in almost any text editor. But one of the simplest and most common is Windows Notepad. Files with the extension .txt are associated with this program by default.
PDF is short for Portable Document Format, which can be translated from English as “Portable Document Format”. It was developed by Adobe Systems for use by US federal authorities as a tool for storing working documents. This is a universal cross-platform format, which is now standard for electronic documents. It serves to convert text files (including photographs or other images) into electronic documents without any loss. To read PDF files you need special programs - Adobe (Acrobat) Reader, PDF-Viewer and others.