Hi Aguarin,
If you are looking to collect these comments/feedback in the registration process, you could drag on a "text question" question type and change the display & format to comment box and attendees would be able to enter in their comments and you would be able to pull them into Cvent reports.
As an alternative, there is a file upload question type that you can also add to the registration process, if you would like them to upload an actual document/file as a part of the registration process.
Adding Event Questions walks through how to add these questions to your registration process.
------------------------------
Julia Plymack
Senior Client Success Manager
Cvent
------------------------------