I'm using ARIAL font in Acad 2008, when I plot to pdf some wehre ARIAL font show very bold, I'm also use flatten commad after that normal text are changed but dimmension and block text still bold.Imran Hai2011-03-16 13:36:34

After using FLATTEN did you spot check the elevation of the text to ensure it is now at zero elevation or did you just assume the command worked flawlessly?

yes' i'm checked, all normal text are changed but dimension text are still bold.
all objects in drawing z axis is 0

Please try to apply the MTextCF - see the tip:
http://www.cadforum.cz/cadforum_en/qaID.asp?tip=962
 
And make sure you embed all used fonts in the PDF options.

Well that's one explanation I have never heard before.  See, it is possible to learn something new everyday about AutoCAD by coming to the CADforum.  Thanks VM.

User these font  Helvetica , Verdana, Tahoma , Segoe UI and Trebuchet MS. if you have any problem then chang its 'z' value