A contractor sent you a DWG and you do not have AutoCAD. Upload it to the CAD viewer and it renders in the browser: DWG, DXF and DGN up to 10 MB, with the drawing deleted once you close it.
A drawing is a harder thing to render than a document, and the reasons explain most of what looks wrong when one opens. Read this before you decide the file is broken.
A drawing points at things that are not inside it
This is the single biggest difference between CAD and everything else. A DWG is frequently a container of references rather than a finished picture.
External references — xrefs — are separate drawings attached by file path. The site plan, the grid, the title block and the neighbouring building are often four files, and the one you were sent is only the first. Nothing was lost in transit: the others were never in the file. This is why a drawing can arrive nearly empty and still be perfectly valid.
SHX and custom fonts are shape files that live in the AutoCAD support path, not in the drawing. Text drawn with one and rendered anywhere else is substituted, so labels shift and occasionally collide.
Plot styles live in a .ctb or .stb file next to the drawing, not inside it. They map colours to pen widths, which is why the same drawing prints hairline-thin in one office and heavy in another.
Model space and paper space are two different drawings
Model space holds the geometry at full size. Each paper space layout is a sheet with viewports cut into that geometry at set scales, plus the title block and the notes. Open the model and you may see the whole site with no border anywhere; open a layout and you see the drawing as it was meant to be issued. Neither is the wrong answer, they are answers to different questions.
The version is six bytes at the front of the file
DWG is a closed format and Autodesk revises it every few releases. The first six
characters of the file name it: AC1015 is the 2000 format, AC1018 is 2004,
AC1021 is 2007, AC1024 is 2010, AC1027 is 2013, AC1032 is 2018. Open a DWG
in a hex editor and you can read your own answer. DXF exists precisely because of
this: it is the documented text interchange format, published so that other software
has something stable to read, and an ASCII DXF opens in a text editor as pairs of
group codes and values.
When the drawing comes up blank or wrong
- Everything sits on a layer that is off or frozen. The geometry is present and not drawn. This is normal in issued drawings and looks exactly like an empty file.
- Proxy objects. Pipes from Civil 3D, walls from an architectural toolset and similar custom objects only render elsewhere if the drawing was saved with proxy graphics enabled. Otherwise you get a bounding box, or nothing.
- It is over 10 MB.
PURGEremoves unused blocks and layers,AUDITfixes broken references, andWBLOCKwrites out just the part you need. Converting to DXF makes the file larger, not smaller. - It is 3D. A solid model rendered as a flat view can read as a puzzle of overlapping lines. That is the drawing, not the renderer.
Working with drawings regularly? The CAD viewer takes DWG, DXF and DGN without an install.