There was a change in the 1.5RC API. The first parameter in the setFont function now expects an iFont rather than a string as I think it was before.
The docs don't really seem to say much but I did find reference to it on the alivePDF website
An example from there is here :
var msg:String = "Lorem ipsum dolor sit amet, consectetur adipiscing elit."
var myEmbeddedFont:EmbeddedFont = new EmbeddedFont( new fontStream(), new afmStream(), CodePage.CP1252 );
myPDF.addPage();
myPDF.setFont( myEmbeddedFont, 20 );
myPDF.writeText(12, msg);
More info here :
http://alivepdf.bytearray.org/?p=440