Use the document management in order to link project related documents to your projects. You can save the documents in your database, or just set a link to your data directory. To control the access to those documents, you can assing security levels to every document and user in the system. This way you can make sure, only allowed users have access to the information. This is an additional module you can purchase in the order process of Xpert-Timer Pro and Enterprise.
Please refer to the manual for further details about the Document management.
This is a screenshot of the document manager: