How do I file the PND 94 form as a DTV visa holder when my income is foreign-sourced?

It may be worth joining a specific group that discusses in detail Thai tax matters. Thailand Tax rules for expats.

You are indeed confused. Under the terminology of the Thai Revenue Department you are neither a contractor nor a freelancer for the purposes of mid year filings using the PND94 form. If you are tax resident in 2025 then you will file between January and end of March 2026 using either form PND90 or PND91 depending on your source of income. Please stop referring to “Thai sourced income” on a DTV. To get the DTV you must not have any “Thai sourced income”. You income paid to you from abroad whilst you are working online is classed as foreign sourced income once you become tax resident. When you bring that foreign sourced income into Thailand in a year you are tax resident or in future years it may attract a Thai tax liability. You will most likely be able to claim a tax credit pro rata based on your remittances against your Thai tax liability depending on the wording of any DTA that is in place. You have until the end of the year to read and research the Thai Revenue Code in relation to PIT charged to remitted foreign sourced income.