Others have already answered your question, but in case you mean something besides "simple text file" when you say "simple text file". What I mean by that is a simple text file is usually just that "simple text" however a document file (or a Rich Text Format, RTF, file) can create bold, italic, or underlined text - this would have to be done through some software's API though that might be possible with perl. I've used OpenOffice::OODoc without problem or search cpan yourself for Microsoft Office or RTF or etc...

This is a very simplified explaination, but I felt doc and rtf types of files should be mentioned