Fix a DWG file that will not open (drawing file is not valid)

When a DWG file is not opening, the cause is almost always one of five things: it is not really a DWG, it is too old or too new for the program, it is corrupt, it is too large, or the viewer environment is missing something. This page walks through the checks in order, from a ten-second header test to AutoCAD's RECOVER, and says what the browser viewer on this page does in each case.

Step 1: check that the file is really a DWG

In a real-world test in October 2026, 14 of 18 user-submitted DWG files opened in the browser viewer. Two of the four failures were not DWG files at all: a ZIP and a PDF that had been renamed to .dwg. That is the first thing to rule out.

1. Open the file in a plain text or hex editor (Notepad works; so does head -c 6 on macOS or Linux).
2. Look at the first six characters. A DWG always starts with AC10 and two digits, for example AC1032.
3. If you see PK it is a ZIP: rename it to .zip and extract. If you see %PDF it is a PDF. If you see 0 and SECTION on the first lines, it is a DXF: rename to .dxf and it will open.

The viewer reports a renamed file as one it cannot read rather than hanging, because the LibreDWG converter rejects the header before doing any work. AutoCAD shows Drawing file is not valid for the same reason.

Step 2: check the DWG version

The two digits after AC10 tell you the format version, and version mismatches cause the invalid or incomplete DXF/DWG input file message in LibreDWG-based tools and the not valid message in Autodesk ones.

Too old: the other two failures in that test were R11/R12 drawings. Open them in Autodesk DWG TrueView, which reads every version, and save as 2013 or 2018 format. Too new: an older AutoCAD or LibreCAD-era tool cannot read AC1032. Ask the sender to SAVEAS an older version, or convert with DWG TrueView's DWG Convert. The full version history is on DWG versions.

Step 3: repair a corrupt DWG

A DWG with a valid header that still fails in every program is probably damaged: an interrupted save, a network drive hiccup, or a crash in a plugin. Repair options, in order of effort:

1. RECOVER in AutoCAD (not OPEN). It rebuilds the object database and reports what it discarded. RECOVERALL does the same for attached xrefs.
2. AUDIT after a successful recover, answering Yes to fix errors, then SAVEAS to a fresh file name.
3. Look for the backup. AutoCAD writes a .bak next to the drawing and .sv$ autosave files in the temp folder. Rename either to .dwg.
4. Insert instead of open. Start a new drawing and INSERT the damaged DWG as a block; AutoCAD reads only the entities and skips a broken header or dictionary.
5. DWG TrueView and the ODA File Converter use different parsers from each other and from LibreDWG. A file one of them refuses sometimes converts in another.
6. Autodesk's drawing recovery service and commercial CAD repair tools are the last resort for a file with no backup.

There is no reliable repair DWG online service that does not upload your drawing; treat any such page as a file transfer to a stranger. The browser viewer here does not repair files; it either converts the DWG or reports that conversion failed.

Step 4: size and environment

• Over 60 MB. The browser viewer skips conversion above 60 MB and says so. Shrink the file with PURGE and -WBLOCK as described in open large DWG files.
• No WebGL. The renderer needs WebGL. On a locked-down corporate browser or a remote desktop session, WebGL may be disabled, and the drawing area stays blank. Try another browser, or enable hardware acceleration in the browser settings.
• Phone memory. Large files on iPhone or Android can make the tab reload. Use a laptop for anything beyond a few megabytes.
• DWG TrueView not opening at all. Usually the installer or a Windows update left the .NET or VC++ runtime inconsistent. Run Repair from Windows Apps and features, or reinstall; if TrueView opens but the file does not, the problem is the file, so go back to steps 1 to 3.
• LibreCAD cannot open DWG. That is by design: LibreCAD reads DXF only. Convert with the ODA File Converter, or view the DWG here and work from the drawing.

What the browser viewer reports in each case

If the file opens here but not in your CAD program, the DWG itself is readable and the problem is on the software side: version, plugins or installation. That alone saves a lot of guessing.

Frequently asked questions