An AFM font alone is not a complete font. It is only the metrics, an ASCII file (you can open it in a text editor) that shows the width, kerning, and some other information on the font. There are two other font files that Type 1 fonts use. In the PC world, one is pfm and the other is pfb, if I remember correctly. You need both of these, and not the afm one at all, if you want the font to work. I can't remember the Mac situation, but I seem to remember it also needed two files.