Consulting and engineering company seeks archiving and document management software

I am looking for archiving and document management software for my consulting and engineering company (engineering services).

The solution should meet the following requirements:

• Legally compliant digital archiving of documents (PDF) and emails
• Audit-proof
• Windows-compatible

This is for a single software workstation. It may be shared between a desktop and a laptop, but never two workstations at the same time.