Well, you certainly seem to be right about having to file, whether tax payment is due, or not:
I haven't yet been to RD, (my office is in Sathorn: Thai Chinese Chamber of Commerce, opposite Surasak BTS).
But in the meantime my office manager has been helping me, by ringing them up to find out whether I need to file (yes, apparently), and how I need to file.
Even though my income into Thailand is less than my TEDA, they still want me to file. I only need to show ATM withdrawal amount, (THB160K) and not credit card, but debit card amounts.
First, I need to apply for a Lor.Por.10.1 (to obtain a TIN). Then I need to complete a Por.Nor.Dor 90. However, having looked at the PND90, it is not obvious how or where I put in the sums and deductions, so yet another (4 or 5 so far) call to inquire.
Anyway, I'm not convinced that I really do need to obtain a TIN, (not as simple as just using my pink ID number, it will apparently be different to that 13 digit number)*, and then I need to file, and I suspect that when I try to get them to answer my question about how to complete the PND90, they may say "not necessary". A further call will be made, and then I will go and see them in person, with my Thai manager.
I didn't think this was going to be easy, and I was right.
*Maybe those who obtained their TIN with a pink ID had to complete this Lor.Por.10.1 form?