CertificateChain.LoadPfx methods load PFX and PKCS #12 files that contain certificate and private key. These usually use .pfx and .p12 extension (not .p7b).
Certificate.LoadDer method loads raw certificate data (DER) and Base-64 encoded DER with header and footer. Certificate files supported by this method usually use .der, .cer, .crt or .pem extensions.
CertificateChain.LoadP7b method loads a certificate chain from PKCS #7 files. These usually use .p7b or .p7c extensions, although PEM variants (.pem or .spc) can be used as well.
Load method loads PKCS #8 private keys that usually use .pri or .key extension. It also supports OpenSSL SSLeay keys and PuTTY keys that use .ppk extension.
SshPrivateKey class supports the same key types as well. (However, some private key files use .pem extension, and some .key files are actually public keys that can be loaded using
Certificate.LoadDerWithKey method loads a certificate (just like
Certificate.LoadDer), loads a private key (just like
Load method) and associates the two.
PVK (a proprietary certificate and key storage format) is not supported by our API.
I am not sure what the "NET" format is and have not been able to find any information about it. Do you have any additional information on this? And how is it related to PKCS #8?