Document management system needed for approx. 50 clients in an auditing company

We are active in the service industry as an auditing company and are looking for an audit-proof document management system that should fulfill the following requirements:

• Electronic client file
• Structured document storage
• Audit-proof (when documents are deleted or changed, a log should be kept)
• Full-text search by keyword, even for image files (via OCR function running in the background)
• Flexible search options
• Resubmission and acknowledgement function
• Confidential files and documents should be protected from unauthorized access by user rights
• It should be traceable who has edited what in the document and when
• Interface to the Cobra CRM system

40 to 50 workstations are planned.