While modern versions of Windows (such as Windows 10 and Windows 11) have excellent multilingual support, they do not always come pre-installed with the specific font files required for every dialect or government standard.
You can find the Phetsarath OT font through several reliable sources: Google Fonts : The modern version of the font is available directly via Google Fonts Official Lao Government Portal : Historically, the font was hosted on the Phetsarath government website : Developers can find the raw files in the Google Fonts GitHub repository LaoScript for Windows download font phetsarath ot for windows