Open Windows Character Map, select vn-vni.shx as the font, copy the accented character, and paste it into AutoCAD. This is slow and outdated.
How to install a new or custom font for use in AutoCAD products - Autodesk tai font vn-vni.shx
While younger engineers often default to Unicode and modern operating systems, the construction and manufacturing industries move slowly. Hundreds of thousands of .dwg files in Vietnam’s infrastructure (bridges, factories, high-rises) still rely on tai font vn-vni.shx for their text annotations. Open Windows Character Map, select vn-vni
To use this font, you must place the file in AutoCAD's dedicated font directory. Open Windows Character Map