Creating a proof of your 3D content in the SketchFab player is as simple as copying the embed link and creating a new proof using the url link function.
To create a SketchFab 3D player proof
In SketchFab, click Embed
In the Embed viewer, select Autostart and any additional options. Click on the embed code to copy it to your clipboard.
Paste into a text editor the embed code and look for the src="......" link.
It will look something like this:
Copy only the content inbetween the quote marks.
In PageProof, click the file dropper icon on your dashboard and click the link icon. Paste the URL link you copied and follow the usual step/s to send your proof.