In my previous post I used the CMS type to open a PKCS7. Apparently X509Certificate2Collection Import method can also be used to open up a PKCS7. This would be far more simpler then using CMS.
Additionally, you might be asked to add the certificates you obtained from PKCS7 file or a serialized store (sst) file to an actual store. Below is an example powershell script to accomplish it:
$certs = new-object system.security.cryptography.x509certificates.x509certificate2collection
$store = new-object system.security.cryptography.X509Certificates.X509Store -argumentlist “AuthRoot”, LocalMachine