If you tell the truth you can have an easier life and not worry about getting caught commiting fraud and facing the consequences. As the Thais say: Up 2 you.
Generally you need to show the same documents at an extension as when you applied for the visa. So to extend a DTV, I'd expect to show up to date documents of what you needed for the visa.
Go to any AIS store in a mall with your passport and they'll set you up in 10 minutes. They might steer you to more expensive service, but ask for the cheap ones.
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