How would you build up a document database in WordPress?

Hey, I have a possible client and the client wants a document database. Such as indexing/searching for pdf-documents and/or word-documents. I was thinking of a smart way of combining categories and custom fields to achieve this. But it would save me some time if there is a good plugin/extension for this. Or maybe if someone has a more flexible and good solution. Maybe its possible to use WP’s attachment for this?

I have been thinking about using custom taxonomies for this. Do you guys have any good ideas or maybe tips?