I was following as long as you were using actual command names, but what does "lock the PDF" mean? How does that change it from a 7.5" x 10" page to an 8.5" x 11"? The default for 2016 is now 16:9, which is not going to fill an 8.5" x 11" without distortion.
I think a better approach is to create custom page sizes that match the PowerPoint slide dimensions:
- In PowerPoint, choose File>Print.
- Change the Page Size dropdown to Manage custom sizes.
- In the dialog, click on the plus sign in the lower left corner. A new page size is created.
- Type in a name like PPT Widescreen.
- Enter 10" for the Width (yes, that's correct, page sizes are always specced with the narrow dimension as the width)
- Enter 13.33" for the Height.
- Set all margins to 0". OK out.
- While you're there, create custom pages for OnScreen (5.63" x 10"), the older 16:9 format and Standard (7.5" x 10").
Now, when you print to PDF, choose the same custom page size as is used to format the presentation and you'll get an undistorted borderless PDF.