This article gives you an overview of what the documents section is for and where you can upload documents.
The Autotrip app has the option to upload documents to support your business mileage claims. Examples of these could include car insurance papers, fuel VAT invoices, driving licence, etc.
Your employer may require you to submit these alongside your report for proof of your mileage. Check out this handy guide on how to attach documents to a mileage report.