Scenario
User has a System Email Template and would like to create an identical Email Template from it.
Solution
The content of the System Email Templates can be copied and used as a Document Email Template.
1. Navigate to Setup > Company > System Email Templates
2. Click on Edit next to particular template
3. Click on Source button to switch to source code
4. Copy the whole content
5. Navigate to Documents > Templates > Email Templates > New
6. Name the template
7. Click on Source button
8. Paste the content from system email template
9. Click Save