GerbView

GerbView is an powerful application that enables you to view, print, convert Gerber, PLT, HPGL/2, Excellon and other file formats. Convert to PDF , DXF, DWF, CALS, TIFF, RS-274X and more.
Gerbview will visualize your design, on the screen or in hardcopy. No more waiting for photoplots or your prototype circuit board, to see your true design.
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, which most PCB producers prefer to receive. The new extended Gerber format contains embedded aperture information, and this minimizes the risk for errors during the manufacturing of the PCB.
Markup elements like text, arrows, lines, images, symbols, barcodes, qr-codes ellipses and polygons can be added to the workspace.
These markups elements can be 'burned-in' to be a part of a Gerber layer.
In GerbView you work with a workspace that can contain one or more files of the supported file formats. The workspace can be saved for later use. The saved workspace will link to your design files, so only need to reload the workspace file to see the whole design.
You can use measure and query tools to get information about distances, areas and apertures.