RAD Studio uses a Java Keystore (.jks) to sign Android apps, not Windows code signing certificates. To sign your Android app, generate a keystore using keytool, then configure it in Project > Options > Android > Provisioning. Windows certs can't be directly used due to platform-specific signing requirements.
Code signing Certificates are mostly for Windows and IOS Apps. You can buy one for an affordable price from here.
signmycode.com