The pdf envelope templates in the links FPCA envelopefit standard business size envelopes (108 x 235 mm) available in Thailand.
The size of the pdf document is #10 envelope, but standard business size envelopes available in Thailand are a bit smaller, hence the bigger margin on the left.
Although the document is envelope size, it works best for us to print on A4 paper, cut out the part with printing, and use a glue stick to paste the part with printing onto the front of the envelope.
You can type or paste in your From abroad address and the To address to which you are sending your ballot or FPCA.
After you put in the addresses, hit Print. On the Print dialog, it helps to choose "Actual Size" and Landscape mode.