Autodesk DWG TrueView 2017 is a free tool for viewing CAD files in DWG and DXF format.
The program can also convert DWG files to formats suitable for earlier versions of Autocad. This might be useful if someone's sent you a file which you're trying to open in another CAD program which doesn't fully support the latest formats.
This isn't a regular lightweight viewer; the download is over 600MB and a full installation needs approaching 1GB of hard drive space. But even if it takes a while, installation is at least easy, with no registration or other hassles.
The interface looks intimidating, at least initially, its ribbon displaying a host of file handling, layer, measurement, snapping and other options. But fortunately you don't have to understand most of that.
Click Open, choose one or more files and they all open in tabs.
Click and drag to pan, and spin the mouse wheel to zoom in and out.
Choose a surface on the "ViewCube" (the navigation tool top-right) and click and drag to spin the model in 3D space.
Click "DWG Convert" to save the file using an older version of the format.
Use the Plot option to print your file, or Export to save it as a PDF.
An accurate and reliable DWG/ DXF viewer. Measurement tools help you extract dimensions, and the file conversion and export options are another big plus.