I forgot my bag with the certificate on the train.
Do I have to show my credentials?
Could I check your ID?
You hopefully know that 証明 means "proof." So, when the proof is written down, what kind of proof is it? It's a certificate of some kind. I'm going to need to see some 証明書 if you want to get in here, sir.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well. Knowing 証明's reading will also be helpful.