You may be able to upload up to 20MB but we recommend 15MB maximum. I recently was able to upload a 12MB file but it really does slow down your portal when uploading a large file like that. If you think you’re going to have some submitters uploading large files like that, you can set a limit on your document and if they really want to, let them know it will be very slow uploading (and if it’s too large, it won’t work).
For large files, or video files, you can ask them to upload it in a different place, Dropbox/Google Drive and then pop a link in instead.
In many cases, large file sizes are the result of large, high-resolution images being used in documents and PDFs and simply asking people to use slightly lower resolution images dramatically reduces the file size. More information can be found here.