There is a 'Documents' area within a clients record. This area records all correspondence with the client. This includes emails such as appointment reminders and booking confirmations. It logs SMS and letters and it also contains any documents that you upload.
When you click on the 'Documents' section it brings up the screen below which shows all the correspondence. You can click the 'Attach a file' area to upload documents that have been made outside of TM3; alternatively you can drag files into this area too.
If you click on any of the listed documents it shows you when it was last modified, who it was created by, the size of it and the ability to 'View', 'Rename' or 'Delete'.