I Need my daughters BC to get her a passport, but the mother has hidden it and i'm no longer with her. I Have photocopies of the BC, is it possible to get a duplicate copy at the amphur where the birth was registered?

I believe you can.

But if it is a Thai passport, you will need the signature of the mother, unless you have sole custody. A lot of countries have likewise regulations. You better check this first.

Also, if you are where not legally married to the mother you in all likelihood will not have legal custody over the child.

New Birth certificate is issued totally free at the amphur where the child is born, you need a valid rason to get a new one, not just want a spare or father wants one to get child western passport (why not use the one the mother has?). Lost it is good reason (police report would be good but may not be necessary, not sure, check)

You are not married to the mother so mother has sole custody, you have currently no parental rights in Thailand. I don't know if a father who doesn't have parental rights can request new birth certificate, maybe not. I bet that if you say mother has hidden it, then they will check in their computers -> mother has sole custody and then refuse you. If you make police report that father and mother has searched and cannot find birth certificate, then go to amphur, perhaps they will issue one.

Good Luck

From your other posts I gather that you are indeed not married, as otherwise there would not be a problem with legalizing the children.

You will have to legalize the child first, if you take the child without the mothers permission even for 5 minutes you can be charged with kidnapping and spend a long time in jail. Even in your own country you could be prosecuted.

I agree, you need to go through the Thai courts to get legitimized. Even if you do get an original birth certificate and you are lucky enough to come from a country that doesn't require other evidence than original BC to get a western passport. Even if the mother agrees at that time, she can change her mind any time later. Mother can sue 5 years later if she wants, if you don't show up at court here in Thailand then mother will eventually get sole custody awarded and there will be an arrest warrant for you issued. Then what? Not good for the child to have a father who doesn't dare to go on holiday to his own childs birth country because he risk being arrested at the airport. Don't think the child would see his birth country very often. A child has a right to both his father and his mother

I really recommend to go through the process of getting legitimized etc here in Thailand - to have all papers clear - No worries ever in the future

Good Luck