The surface model contains many opening which prevents the you to create a "water tight" solid model. It would take some time to edit this file to create a solid model. Did you receive this file from a vendor or did you get it from a web site? I would be better to see if you can get the contact the manufacture to see if you can get a new file. Asking for a STEP file.
HELLO, SEE ON THE BROWSER APPEARS A SURFACE ICON. IF IT APPEARS CLICK THE MOUSE RIGHT BUTTON AND CHOOSE REPAIR BODIES. IN THIS ENVIRONMENT YOU USE THE FIND ERRORS TOOL TO FIND AND CORRECT POSSIBLE GAPS FROM THE SURFACE. IF THE INVENTOR CAN CLOSE ALL GAPS, USE THE STITCH TOOL TO SEW SURFACES AND CONVERT TO SOLID. IF THIS DOES NOT HAPPEN YOU HAVE TO MANUALLY CLOSE THE GAPS ON THE SURFACE AND THEN SEW. IF YOU CAN'T, SEND ME THE FILE I MAKE FOR YOU. HUGS