To create an HTML version of a drag and drop style template built in HubSpot, navigate to Content > Design Manager > locate your template under the Templates folder, or by searching for the template by name > click on the name of the template within the template list to open it in edit mode.
With the template open in layout mode, click Actions > Clone to file.
In the Clone to file popup box, give the template a name (or leave as is) > select a Save location > and click Clone to finish.
Your cloned template will now appear in the Design Manager > Coded Templates > Custom > whichever sub-folder you selected > as your_cloned_template_filename.html.
The template file will not be exported to your HubSpot file manager.