1.       Open the MMC (Start > Run > MMC).

2.       Go to File > Add / Remove Snap In

3.       Double Click Certificates

4.       Select Computer Account.

5.       Select Local Computer > Finish

6.       Click OK to exit the Snap-In window.

7.       Click [+] next to Certificates > Personal > Certificates

8.       Locate and select the certificate for the correct domain. 
Right Click and select All tasks > Export.

9.       Press Next

10.    Select Yes, export the private key.

11.    Choose Personal Information Exchange - PKCS#12 (.PFX) for the certificate file format. Check the boxes for: 
Include all certificates in the certificate path if possible
Export all extended properties 
Click Next.

12.    Enter a password for your private key. Press Next.

13.    Click browse and save your .pfx

14.    Press Next > Finish > OK.