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Navigate to Personal Certificates:
In the MMC, expand the tree for Certificates (Local Computer) or Certificates - Current User.
Right-click Personal > All Tasks > Import.
Certificate Import Wizard:
In the Certificate Import Wizard, select your client certificate (.pfx or .p12 file).
If the certificate is protected by a password, you will be prompted to enter it.
Mark Key as Exportable (must):
During the import process, make sure to check Mark this key as exportable if you may need to export the certificate later with the private key.
Complete the wizard, and the client certificate will be added to the Personal store.
