This depends on the font. The opened drawing makes use of AutoCAD fonts. Anyone in possession of a regular AutoCAD license can also use the fonts supplied with AutoCAD in the progeCAD program along with the numerous fonts already available in progeCAD.
Just open the Tools > Options menu and access the Path/File tab > Support paths sub-menu. Double click Fonts and add the fonts installation path. For ex.: C:\Program Files\AutoCAD R14\Fonts.
For the 2000 version of AutoCAD the simplex font can be found in Support directory. You can add this path too (For ex.: C:\AutoCAD LT 2000\Fonts;C:\AutoCAD LT 2000\Support) or copy this font to the folder Fonts of AutoCAD 2000.
This guarantees a perfect display of any project using the simplex.shx font.