Unknown Characters in Thai Fonts When Viewing PDF Generated from InDesign in Acrobat

Hello Acrobat Community, I've been having issues regarding the files exporting from InDesign and viewing the PDF in a browser using Acrobat Reader and Adobe Acrobat.

At early stage, I thought it's errors on InDesign part as I mention in my post here. I use Thai fonts and the exported files looks perfectly fine, but if I copied&pasted it on Notepad or using ctrl+f funtion to look for keywords, I coundn't find a single match as all the fonts are in the wrong orders with unprocessed glyphs or unknown characters as attached.

This causes us lots problems as we want to spread knowledge and info to all audience, but our work has never been showed up on the web browser because they cannot find the matching keywords by the search engine.

After the generous help from InDesign Community, I did some new setting and adjustment but the problems persist. And we tried using the same text and fonts on Illustrator to compare and the issue reduces significantly but some issues remain the text copied from Acrobat Reader.

We conclude that the problems may arise from Acrobat part and hope that the experts here could help. I would love to continue using InDesign but the issues are truly diminishing value and impact of our work.

Thank you in advance.