ExeScan not only allows you to add scanned, faxed and emailed documents to it's database but now you can add any document. It works as follows: 

You install a simple 'ExeScan Print Driver' that you 'Print to' from your application. Instead of the page being printed in the traditional sense, it gets posted as a TIFF file straight into ExeScan where it can be indexing and saved away. Simple and it works brilliantly.

See www.exescan.co.uk/tiffprinting.html for more details.