For internally developed applications, we would not want to buy digital certificates and sign the InfoPath form templates using them. Hence comes the concept of self signing the form templates. However this has to be used strictly for testing purposes only.
1) Download the Microsoft Platform SDK for Windows Server 2003 R2 from Microsoft site.
2) Use the makecert utility located in the C:\Program Files\Microsoft Platform SDK for Windows Server 2003 R2\Bin folder.
makecert -sk <key file store location name> -n "CN=TestCertificate for Himani" certificate1.cer -ss my -pe
3) Now the certificate will be available in the “personal folder. You can use signtool.exe’s signwizard to sign the form template with this certificate. You need to select the certificate from the personal store and select the private key store location.