if you want only the text from a document (pretty much any document: RTF, Word, PDF), you can try
set theFile to choose file with prompt "Select a text file:"
tell application "TextEdit"
set myDoc to open theFile
set theFileContents to the text of myDoc
close myDoc
end tell
return theFileContents
to retrieve it.
But then all formatting beyond line breaks will be gone. Is that what you want?
Else, you will have to handle formatting in RTF (which is less daunting than is appears) or transform the text to HTML or so...
Cheers
Thomas