How to change certificate file format

Using a text editor

1. Open the received file in a text editor.
2. In the editor, click File → Save as... or use the keyboard shortcut Ctrl + Shift + S.
3. When saving, specify a file name and the desired extension.

Repeat these steps for other files if necessary.

Via OpenSSL

Convert files to PEM format using the command:

openssl OLD_FILE_FORMAT -print_certs -in OLD_FILE.EXTENSION -out NEW_FILE.EXTENSION

Example:

openssl pkcs7 -print_certs -in certificate.p7b -out certificate.crt