I just typed 'text formats' in a search engine. Here's the first result

http://dio.cdlr.strath.ac.uk/standards/fileformats/textformats.html

(There were about 41,300,000 others)

Text can be in many, many, many different formats. It's actually relatively easy to create a new file extension that works just like a plain text file (.txt)

And it depends on what you mean exactly with "formats in which text may be presents". An HTML file (.htm or .html) is basically just text too, but has a different purpose. The only real difference between a plain text file and a webpage file is its extension, which is to allow the system to react accordingly when either file type is opened (.txt will open in a basic text editor by default, and .html in your web browser). That's basically the only reason why file extensions exist.

http://iq.lycos.co.uk/qa/show/53033/