Open the folder which holds the certificates you have downloaded.
Right-click on the certificate you wish to install, and select Install PFX from the context menu.
Click the Next button in the Certificate Wizard welcome window.
Click the Next button in the Select File to Import window.
The personal e-mail certificate files created by PHPki contain an encrypted copy of your private key. When your certficate was created, a password was given to PHPki to encrypt the private key. The same password is used to decrypt your private key and install the certificate. Do not forget or lose this password as it cannot be recovered under any circumstance. Select the Enable strong private key protection option if you would like Windows to add an additional layer of password protection to use your certificate. This is not necessary, and will not be covered further here. There is no need to select the Mark the private key as exportable option. Enter your certificate password and click the Next button in the Password Protection for Private Keys window.
Click the Next button in the Select a Certificate Store window.
Click the Finish button in the Complete the Certificate.. window.
Windows confirms the root certificate was successfully imported.