FreeCAD and DWG Import

Why is it hard to support DWG Files in FreeCAD?
The DWG format is a closed source binary file format that is not directly supported by FreeCAD. It requires an external 3rd party file converter to first convert then import the conversion into FreeCAD for use.

Note that at this time, it is not possible to import 3D DWG in FreeCAD. 3D data is embedded as binary .SAT (ACIS) data, a proprietary and undocumented format.

ODA Converter (formerly Teigha Converter)

 * homepage: https://www.opendesign.com/guestfiles/oda_file_converter
 * license: freeware
 * optional, used to enable import and export of DWG files

The ODA Converter is a small freely available utility that allows to convert between several versions of DWG and DXF files. FreeCAD can use it to offer DWG import and export, by converting DWG files to the DXF format under the hood,then using its standard DXF importer to import the file contents. The restrictions of the DXF importer apply.

Installation
On all platforms, only by installing the appropriate package from https://www.opendesign.com/guestfiles/oda_file_converter. After installation, if the utility is not found automatically by FreeCAD, you might need to set the path to the converter executable manually. open Edit → Preferences → Import-Export → DWG and fill "Path to Teigha File Converter" appropriately.

For more detailed instruction see this tutorial.

Usage
The program may be used with the command line interface or the graphical interface. Be sure to convert the DWG files to an ASCII-Format.

Command Line Format is:
 * 1) Quoted Input Folder
 * 2) Quoted Output Folder
 * 3) Output_version {"ACAD9","ACAD10","ACAD12", "ACAD13","ACAD14", "ACAD2000","ACAD2004", "ACAD2007","ACAD2010"}
 * 4) Output File type {"DWG","DXF","DXB"}
 * 5) Recurse Input Folder {"0","1"}
 * 6) Audit each file {"0","1"}
 * 7) [optional] Input file filter (default:"*.DWG;*.DXF")

Example for Linux

ODAFileConverter "/home/dwg-data" "/home/dxf-data" "ACAD2010" "DXF" "0" "1" "test.dwg" The second number (audit) needs to be 1 otherwise it fails

Example for Windows

"C:\Program Files\ODA\Teigha File Converter 3.08.2\TeighaFileConverter.exe" "Path-To-Input-Directory" "Path-To-Output-Directory" "ACAD2010" "DXF" "0" "1" "Name-Of-A-Test-File.dwg"

FreeCAD v0.19 and LibreDWG

 * homepage: https://www.gnu.org/software/libredwg/
 * license: GPLv2-or-later
 * optional, used to enable import and export of DWG files

GNU LibreDWG is a free C library to handle DWG files. It aims to be a free replacement for the Open Design Alliance Drawings SDK libraries.

Installation
LibreDWG is included in v 0.19_pre appimages

LibreDWG can be configured to work on Windows by downloading and unzipping the appropriate pre-compiled windows binary and adding the folder to your Windows versions system path.

DoubleCAD XT
There is also DoubleCAD XT (https://www.turbocad.com/content/doublecad-xt-v5). The program is free for personal and commercial use. It requires a free sign-up to receive an activation code via E-Mail. This Program is windows-only. Note: it does not seem to have been updated for years.

Export Your AutoCAD files in Friendly Format
Exporting your AutoCAD files in a more FreeCAD friendly format, like DXF R12 or R14, SVG, and if version supports it, IGES. All are better alternatives to the DWG format when using FreeCAD.

It is important to know that, contrarily to popular belief, there is no difference between the contents of a file saved in DWG or DXF formats, provided it is the same version (ex. DWG 2014 vs. DXF 2014). Both formats are maintained by Autodesk, and they both support exactly the same features. The difference is that DWG is closed (machine-encoded) while DXF is open.

Promote the use of alternative formats
Simply put, stop accepting work done in DWG format. In practice, this is often easier said than done. Still, it would not be bad practice for users and supporters of FreeCAD to avoid and reject the DWG format whenever possible.

Use the LibreDWG library and file bug reports
In development version as mentioned above you can switch from the proprietary ODA Converter to the free software LibreDWG library for DWG (and DXF) files. Please do this and report any problems you encounter.