DWG

DWG is the file format AutoCAD saves drawings in (.dwg). One file holds the model space geometry, one or more layouts, blocks, layers, text and dimension styles, links to xrefs and, in Plant 3D, the piping and equipment data.

The format changes every few years. The versions you meet most are R12, R14, 2000, 2004, 2007, 2010, 2013 and 2018, and a drawing saved in a newer format cannot be opened by an older AutoCAD. To send a drawing to someone on an older release, save it in an earlier format: the 2010 format opens in AutoCAD 2010 and everything after it, the 2018 format in AutoCAD 2018 and later.

DXF is the other common drawing format. It is openly documented and easier for other software to read and write, while DWG is more compact and is what most CAD users exchange. Converting between the two is routine when a program supports only one of them.

You do not need AutoCAD just to look at a DWG file. A free viewer opens it, lets you switch layers and layouts, measure, and print or export a PDF. The CADXChange DWG Viewer does this in the browser or as a small desktop app, and the file stays on your computer. Other CAD programs also open DWG files, but dynamic blocks, custom objects and fonts may not look the same as in AutoCAD.

If a DWG file will not open, the usual causes are a damaged file, a format newer than your software, or a drawing that needs xrefs and fonts it cannot find. The second-generation CADXChange tools read and write DWG files directly, so batch editing, comparing, searching and plotting do not need AutoCAD installed.