Simple steps to do this:
1)Create a Font css file (give the font file name and font family name that you would use in your flex app)
eg:abc.css
"@namespace s \"library://ns.adobe.com/flex/spark\"
"@namespace mx \"library://ns.adobe.com/flex/mx\"
"@font-face {
src: url("AGaramondPro-Regular.otf")
fontFamily: "AdobeGaramondProRegular"
embedAsCFF: true;
}
2)Convert it to swf using mxmlc compiler.
mxmlc [options] abc.css
This compiler resides as yourflashbuilderdirectory/sdks/4.0.0/bin/mxmlc.exe
Note:You may get some error related to msvcr71.dll while compiling, so please copy the same from java/jre(your version)/bin directory to the mxmlc directory.
3)load this font swf at runtime
StyleManager.loadStyleDeclarations (path to your font's swf)
Once this swfs get loaded the fonts get embedded and registered automatically.