Canon EOS-1D X Mark III Advanced User's Manual page 604

4.
Select [Set root certif].
5.
Select [Load root certif from card].
6.
Select [OK].
The root certificate is imported.
Select [OK] on the confirmation screen to return to the [Set root certif]
screen.
Note
To delete the root certificate imported to the camera, select [Delete root
certificate] on the screen in step 5. To check who it was issued to and issued by,
the period of validity, and other information, select [View root certificate details].
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