The Template Preview functionality of the DocumentsCorePack Template Designer allows you to see a thumbnail of your templates when opening or saving them.
This new feature requires at least version 9.25 of the template designer and version 2017.184 of the server or service. 
The preview section (1) is embedded at the right hand side of the open or save Template Dialog 

Figure 1: Preview Section

You can enable or disable the preview you using the magnifier icon in the control menu bar (1).
By using the "View Detailed Image" (2) you can enlarge the thumbnail to its full size. Additional scrollbars will allow you to view the enlarged image.

Figure 2: Preview Controls

There are only preview images available for templates that are saved since the new required version was installed. Any old templates will not have a preview yet. 
If you completely want to remove this functionality please set the following settings key for DocumentsCorePack manually, like described here, with the below key name and value.
Name: DisableTemplatePreviewImageUpload
Value: true

That’s it! We appreciate your feedback! Please share your thoughts by sending an email to support@mscrm-addons.com. 

Related content:
Template Versioning (Dynamics 365)​
DocumentsCorePack Template Designer - New Features