How do i use export as file to export as PDF instead of PNG

Question

When I use Export as file (Clt + E), the default output is PNG, how do i change it to PDF?

Stefanos Papavasileiou · Accepted Answer

Dear Kai Xiang SEE, 
 I would instead use the Print option (Ctrl + P) and set my printer to PDF. 
 The export functionality only allows saving as a PNG as it is a visual plot being exported.