With the help of this article you can troubleshoot opening Tresorit DRM-protected files in Office 2013.
Step by step manual on opening DRM protected files.
1. Please open an empty Microsoft Office document and search for your credentials that can be found in the upper-right corner in case you have a logged in user
2. Click on <Switch account> and then <Add Account>
3. Open the Tresorit app and check your DRM credentials here after clicking on <Settings> and scrolling down:
4. Click on <Show DRM credentials> and then copy the first line (the username)
5. Paste the copied text in the <Sign in> field:
6. Paste the password (the second line in the DRM credentials) and log in.
Hopefully with the correct credentials you'll be able to open the DRM protected documents.
Office 2010: If you get any other error message, your system may not be up to date. To install all components needed for Tresorit DRM in Office 2010 please refer to this article: https://support.tresorit.com/hc/en-us/articles/216113787-Cannot-Open-DRM-files-in-office-2010
For more information see: