Hi,
If you've added a custom File Upload field to a module layout, you may have noticed it doesn't appear under the "During" transition tab in Blueprints.
Here is a quick workaround to require documents before moving to the next stage:
Go to Setup > Process Management > Blueprint and select your transition.
Go to the During tab on the right side.
Under Associated Items, check Attachments.
Check Make it mandatory.
Save and Publish.