That’s it! Now, when somebody uploads a file through your form and sends it, the file will arrive in your Dropbox account. Other than that, uploaded files will behave normally they will be sent to you via email as attachments (when the file size is smaller than 5MB) or as download links (when the size is larger) and will appear as download links in the Submissions section of your 123ContactForm account.
The file formats that can be sent through the Dropbox integration are all those that are normally supported by 123ContactForm web forms. Find the list of supported file formats here.