Does the Amphor keep my marriage certificate after registration for Kor Ror 22?

My local Amphor retained all the paperwork during the Yellow Book and ID card application, but only for the duration of the application process which took around 1-½ weeks.

Be aware that your Amphur may try to retain the original MoFA certified copies instead of simply taking copies of them for their records.. which is outrageous imo since you may need to use them elsewhere in the future.. and you won't want to have to repeat this exercise and incur further unnecessary expense.. i pushed back hard and told our Amphur they could only keep them if they gave me a legal undertaking to return them if i needed them.. or alternatively, agreed to pay an agent the necessary fee to produce another set for me.. and after deliberation and consultation with superiors they backed down and simply took copies which they had us certify.. this was in San Sai, Chiang Mai, but of course your Amphur could be different!

No the Amphor does not keep your marriage certificate.