Allow Visitors / Members to Upload and Attach File on OptimizePress

OptimizePress does not have any elements that allow visitors to upload files because of security concerns.

You can however use Gravity Form, Contact Form 7, or any other 3rd party WordPress plugins that allows file uploads.

For Gravity Form:

https://www.gravityhelp.com/documentation/article/file-upload/

For Contact Form 7

https://contactform7.com/file-uploading-and-attachment/