Brother MFC 9840CDW - Manual (Page 168)

Security features
158
14
How to export the certificate and private key
14
a Click Export Certificate and Private Key on the Configure Certificate page.
b
Enter the password if you want to encrypt the file.
Note
If a blank password is used, the output is not encrypted.
c Enter the password again for confirmation, and then click Submit.
d Specify the location where you want to save the file.
e Now the certificate and private key are exported to your computer.
Note
You can import the file that you exported.