I tried to install the Circular std font at my Autocad, but when I use it the letters disappear. I have no issues with any other fonts.

[mcgooliveira]

Screenshot of the issue ^

[pendean]

You seem to just have a color problem inside the MTEXT editor, not much else: highlight and change them away from color 255 to like RED or GREEN and see for your self.

[mcgooliveira]

Tried changing the color but didn't work. I think it's more likely to be a compatibility issue 

[pendean]

@mcgooliveira As far as I know, an incompatible FONT type would never even show up on the list, but there it is in your pulldown list.

[dmfrazier]

Do they disappear, or do they become extremely small?

Text size?

Annotation scale?