What are the formats of text files?

Text only (txt) – universal format, small informational volume, but text formatting results are not saved.
Extended text format (rtf) is a universal format, a large amount of information, but the results of text formatting are preserved.
Word document (doc) is a universal format that fully preserves formatting.
OpenDocument Format (ODF) is an open document format for office applications. Web page (htm or html) – a universal format, used to store web pages, a small amount of information, but formatting is preserved.
Portable Documents (pdf) is a format used to reliably present and exchange documents, regardless of software, hardware or operating system.

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