The Australian DTA (and presumably others) says that the country that issues the state provided pension is the one that collects the tax.
You cant opt out of this arrangement, which is unfortunate.
It does however leave the pension recipient, assuming no Thai income, with no Thai tax obligation.
But........ to be tax resident in Thailand you still need to file a return, get a tax id number and fill out the form for tax residency. Do not believe those that say 183 days here gives you tax residency. It's simply not true.
I tried a couple of times, with a few months in between, to file at the Revenue office. Got the same guy both times, and he just refused to do it.
Anyone know an English speaking accountant in Jomtien, or Pattaya?