When using the Letter Template Creator you may receive a message that asks:
"Do you want to open or save this file?"
(See screenshot below.)
This stops normal usage of the Letter Template Creator Editor.
To fix you need to dowload and run the following REG file:
http://www.medilink.com.au/Office%20Docs%20in%20Browser.reg
Click on the download once it is complete, allow all changes when prompted.
Restart the Letter Template Creator and the issue should be fixed.
2019 R2 Update:
You can now fix it from this button inside the Letter Template Creator directly.