If you have a document that is already prepared with template placeholders, and you would like a different document to have the exact same placeholders, you do not have to create them all over again.
You can simply copy the original template;
then click 'Edit';
then scroll to the bottom right and click 'Change Original File';
This will change the original document behind the copied template.
For a step-by-step look at how to do this, please see the following video: