How secure are the files that i share with non-Document management users?

You can password protect your files that you share externally with others outside the organization. This will ensure that your files are secure and being accessed by the right person. On password-protecting your file the person with whom you have shared the file with can access it only on entering the correct password. They can get the password only through a mail request to you. Only if you give the password can they access the document.