>>It sould be possible if you can find where actual document starts in a General field. For example, PDF always starts with '%PDF-'.
>
>Wow, this works. Does anyone know of the marker for a Word and an Excel file?

Looking at a few Excel files I got lying around, it seems that 0hD0CF11E0A1B11AE1, then a bunch of null bytes, is at the beginning of each... same for Word (.doc, .dot). See if that works.