I have two accounts, one free and one PRO, can you transfer files from one to another?

No, due to security reasons, only the owner of the account has access to the account's files. In order to transfer them, you have to log in on the old account, download the files to your local computer and log out. Then log in to the new account, open the files from your computer and save them to the Cloud via "File > Save to Cloud...".