How to convert 3D PDF
to USD?

3D PDF is a PDF file with 3D geometry inside. Using any 3D PDF enabled viewer, rotation, zoom and part selection is available within the 3D view.

3D PDF is just like a normal PDF (Portable Document Format) file, which contains a 3D view somewhere on some page. Just like a PDF containing an embedded image, except when you put the mouse over it, you can rotate, zoom, pan and explore the scene in 3D (three dimensions). The file actually contains a 3D geometric representation of the scene, not just images from different viewpoints.

USD (Universal Scene Description) is a framework for interchange of 3D computer graphics data, created by Pixar. The framework focuses on collaboration, non-destructive editing, and enabling multiple views and opinions about graphics data.