Try to import from Terminal instead of the GUI Keychain Access App.
security import certificate.pfx -k ~/Library/Keychains/login.keychain -P \$tup1dP@ssw0rd
The \ prior to the $ in the example password is called an escape character because $ has special meaning on the command line you need to escape it with \$. If you use an & you would have to escape that as well \&.
To import to the system keychain you'll need to use 'sudo' and that means you must be an administrator and have sudoer privileges.
sudo security import certificate.pfx -k /Library/Keychains/System.keychain -P \$tup1dP@ssw0rd
If your "certificate name.pfx" has a space in it. You'll need to enclose it in single or double quotes or escape the space in the name like certificate\ name.pfx.
