This is a Thai form. My experience renewing my Belgium passport in Thailand the Belgium embassy gave me a letter stating the reason for issuing. They told me immigration would require the letter. Which they did. I stated this before and many people have thanked me as they needed it also.
The easiest way is to go to a visa agent. Yes it will cost you but everything will be done. No worries. It is true you can do it yourself for a lot cheaper but you probably end up fustrated. From the second year do it yourself very easy then
The first priority is filing a police report for lost documents. The next important is your passport as you will not be able to get a new bank book(passport) without passport. I renewed my Belgium passport a few years ago and when they issued a new passport they gave me a letter stating the reason for the new passport which immigration required. With the new passport and letter everything was in order with immigration for them to stamp the new passport.