Are uploaded files secure?

Hi.

If I create a file upload form with "Upload file" feature. Is the file sent and stored securely (https etc.)?

Yes, uploaded files are stored securely. 

Keeping Your Uploads Secure

More about security you can find here - https://www.jotform.com/security/ 

Inside of this guide, you can find how to create a file upload form:

How to Create File Upload Forms