Have you ever spent days or even months developing a map with custom labels using fancy shields in ArcGIS only to have the resulting customer call you saying the labels are all messed up on the PDF you exported out of ArcMap. This is because when ArcMap exports the PDF it assumes the PC you are going to view the PDF on has the same TrueType fonts as the PC where you made the PDF. Under the format tab on the Export Map to PDF form, there is a checkbox to embed the TrueType Fonts. If that doesn't work you can also install the missing fonts on the computer having the issue.