A .skp file is quite different from a .pdf. Basically it’s converting from 3D to 2D? At first glance this sounds impossible. Is the resulting file a useable 2D pdf? Maybe you had better explain your process for sharing the file. You take the .skp file from your hard drive and drop into your google drive?
Can you put a .skp file in a google drive folder and post the link here, let us have a crack at it.
To me, it sounds like the recipient’s computer has the file extension SKP associated with whatever application they have installed that is associated with the PDF file extension.
Ask the recipient to confirm the SKP file extension is associated with SketchUp.