Paperless office / File Management Macintosh software?

I would appreciate any opinions on Macintosh software for viewing/organizing/tagging file archives. Also any un-recommendations (software you do not like).

I am working with someone to scan his paper records so we can get rid of the boxes of documents cluttering his office. We will scan to PDF and we will also be saving old MS Word documents to the same location.

The files will scanned to shared network drive using a Windows machine. The files will then be used by a Mac and two Windows machines.

Note: he really likes Paperport for Windows on his ancient laptop, especially the thumbnail views.