Short answer
HubSpot's KB: the file size limit for a file upload field is 100 MB for both single and multiple file upload fields, and multiple file fields have no limit on file count as long as the total stays within the limit. Uploaded files are stored with the submission and the contact's property. A required field can't be set as hidden.
1. Field types
The Add to form panel in my demo portal; File is further down the list.
2. Use it carefully
- Ask only for files you need.
- Tell visitors the size limit.