How to copy RFID TAG

Hello
Is it possible to copy an RFID tag?
I would like to copy the RFID tag to open the door.
Is there a tutorial?

Do you have a machine to read and write to a writable RFID tag?

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There are many different types of RFID tag, some you can copy and some you can't.
What sort do you have?

You have to start by saying why you want to do this. Most people who want to do this want to do something illegal. We are not into that here.

If you want to open a door and it is legitimate why not get the person who owns things the other side of the door to issue you with a tag, or do you want to steal things?