Management consultancy seeks solution for audit-compliant accounting

We are a management consultancy and have been creating our invoices using MS Office products. We are looking for a simple software solution that supports us in creating audit-proof invoices. We are considering both an invoicing program and a document management system.

The software should meet the following requirements:

• Creation and/or archiving of approx. 20 invoices per month
• Compliance with the principles of proper management and storage of books, records, and documents in electronic form, as well as data access
• Windows-compatible

This involves one software workstation.