can I use Teamviewer to open my files and folders on another computer online
Check "File transfer" menu item in (upper) menu/toolbar (when you are connected).
It opens 2 panels like file manager, where you can see and manipulate local and remote file system (each in separate panel). You can use it also to browse and transfer files within the file system on remote mobile smartphone.
Teamviewer also supports clipboard (cut & paste) on file level. Try Ctrl+C on source file and and Ctrl+V in destination folder.
Otherwise... if you don't need to copy files from remote system to local, you can open files on remote system anyway. Just as like you are sitting at remote system... Double click (or open with Enter) the file selected on the remote system... and wait to see the remote system launching the associated app to cope with opened type of file.
