HOW can I change CAD fonts .shx to LibreCAD fonts .LFF?

In  LibreCAD ,When   I open  A  DXF file  create  in  AutoCAD ,  Some fonts  can ont show Correctly.   I  think  change  fonts in SHX  format  to  LFF  format. and  add the LFF  file  to  Librecad  fonts dir.

Hello. I suppose that you are operating under windows.
My suggestion:

A
I don't know if Autocad has its own converter from shx to ttf, if this is the case, just convert it and start from point 3 of B down here.

B
1 You have the shx file, let's call it "example_font.shx". But you want "example_font.lff"
2 Search on internet "example_font.ttf"
3 Download ttf2lff here   http://sourceforge.net/projects/librecad/files/Windows/
4 Look in this forum in Tutorials/Manual topics "Using ttf2lff for windows" by Rallaz.
5 Follow the tutorial istructions.
6 Copy the font to LC font folder
  (or give the "example_font.lff" path to LC in Edit>Application Preferences>Paths)
7 Enjoy your example_font.lff font on librecad!

In case you are working under another O.S. the steps are similar.
I hope I have been useful.

Best regards
Claudio