What is a .potx file?
.potx
That would be a template file for PowerPoint. All of the designs, backgrounds, programmed colour chips, default fonts, pre-set builds and transitions, saved in an empty slide deck.
PowerPoint 97 and PowerPoint 2003 saved the template with the extension .pot
PowerPoint 2007, 2010 & 2013 save the template with the extension .potx
Below is an example of a PowerPoint 2010 .potx file. Save a copy of it on your hard drive, either in Microsoft’s default location, or anywhere you will likely be able to locate it easily. You can also overwrite the default.potx file with your new template. Each time you open a blank presentation, it will bring in your new style as a blank base.
Next time you open a slide series that follows your old style of slides, you can apply this new template quite easily.
I have found that the easiest way is to open both the new template file and the old series of slides that needs converting. Set both files to slide sorter view. Use the “Arrange All” option under the view menu to see both presentations. Then simply drag the slides you want into the new template set (and save it as something else). Keep an eye out for that tiny paste option fly-out menu, and choose “use Destination Theme”.
Pasting in PowerPoint – use destination theme
Then it’s a matter of tweaking a few text boxes, image locations, or clicking on the “Reset” button (“Home” tab / “Slides” section / “Reset” button)
Champagne Design — PowerPoint Design 