Full Error Message:
Insufficient Privileges: You do not have the level of of access necessary to perform the operation you requested.   Please contact the owner of the record or your administrator if access is necessary.

App Support Reply:
First you want to ensure the user receiving error message is an assigned user to the app. If they are, then that user may see this error when trying to generate document if they have strict permissions on their profile that is causing restricted access to the app components and objects in use to trigger document generation. The user should have A5 Documents classes and VisualForce pages enabled on their profile.  You can create a permission set for this user and allow them access to the following components: Document Action, Document Request, A5 Documents VisualForce pages. After creating this permission set, the users should be able to create documents without the error.