Open a command line with admin rights. (Search for CMD, right click the top result, and select Run as Administrator)
To import a P12 file please navigate to the folder that contains the file and type "certutil -csp "the name of the CSP" -importPFX "PFXFile" (e.g. certutil -csp "Microsoft Base Smart Card Crypto Provider" -importPFX "demo.pfx").
Follow the prompt and enter the certificate PIN.
Enter the smart card PIN
After the successfull import the message "Certutil: -importPFX command completed successfully." will be displayed.