I need send a PKCS12 file to server in Angular client app to sign a PDF in server side (Spring Boot). How safe is send a password protected PKCS12 file over the network. Thanks in advance.
The pkcs12 is protected with a password that is used to encrypt the content, in addition, the private key can also have an additional password, so you can consider it safe.
Use also an SSL encrypted channel to send the content securely and avoid Man-In-The-Middle-Attacks
Note that private signature key should always be under user control and should not be sent to a third party by network.
Depending on local legislation, a digital signature made by a third party that is not considered as a Trusted Service Provider may not be considered valid. Usually, when a signature is performed by a TSP on a server, the key has been securely generated by the TSP in an HSM (cryptographic hardware), and the user is required a second authentication factor, for example an SMS with an OTP