GerbView is an advanced but easy to use application that enables you to
view, print and convert Gerber, ODB++, Adobe PDF, Excellon and HPGL/2
files.
GerbView supports both RS-274D and RS-274X Gerber formats, and you can
use it to convert your older Gerber files to the new RS-274X standard
format. The new extended Gerber format contains embedded aperture
information, and this minimizes the risk for errors during the
manufacturing of the PCB.
With GerbView's PDF to CAD capability you can convert your Adobe PDF
files back to Gerber or Autodesk DXF.