DWG Files

What is a .DWG file?

The main type of DWG file is an Autodesk AutoCAD Drawing Database file and is a type of native drawing file for AutoCAD used after its first release in 1982 in December of the year. Autodesk provides the leading types of the DWG formats which contemporary AutoCAD version from 2018 till 2026 employs the AC1032 family of drawings.

A drawing database file may include: DWGs can include two dimensional geometry or three dimensional geometry. It can include various entities like solids and surfaces and other items like hatches, texts, view ports, layers, layout, block references, external references, plots, tables and other application defined entity data items. It acts like the editable native CAD file while PDF files, DWF files, DWFx files and images resulting after plotting act as delivery or review files. DXF represents the exchange type of Autodesk CAD file format.

DWG files can be viewed in CAD in a variety of professions including architecture, engineering, construction, surveying, manufacturing, facilities management civil design etc. Apart from the AutoCAD programs, several cad products support DWGs using Autodesk RealDWG, ODA libraries or by independent translations, these represent various flavors of the same DWG files not any separate unrelated extensions.

Any valid DWG file usually starts with AC1009 or another version code of AutoCAD. ACxxx is followed by binary content that could not effectively display in a normal text viewer. Very old drawings may have different type versions than ACxxxx versioning and in order not to mistake a certain extension you should examine your drawing by using a CAD viewer, file utility or AutoCAD RECOVER function.

How to open a .DWG file

Technical details

DWG is a proprietary binary CAD database format, neither ZIP nor text one. The first bytes with zero offset in the modern files are composed from a string of six ASCII characters as AC1032 and then followed by binary database fragments; usually, this is represented as 41 43 31 30. Identifiers of different versions indicate various generation families of the format: AC1009 for AutoCAD R11/R12, AC1012 for R13, AC1014 for R14, AC1015 for 2000-2002, AC1018 for 2004-2006, AC1021 for 2007-2009, AC1024 for 2010-2012, AC1027 for 2013-2017, AC1032 for 2018-2026, accordingly.

A drawing is stored as a collection of database items, which contain handles, references to other items (ownership). Standard fragments comprise tables of such as: layers, linetypes, text styles, blocks in addition to model space and paper ones, entity fragments, dictionaries, classes, xrefs, plotting settings, previews and more. Modern version of the DWG employs a set of binary compressed sections, the object map fragment, as well as the CRC-check algorithm; part of the files might be protected with the help of the obfuscating methods too. That way the modification of a DWG via hex-editor usually ruins the drawing.

Mostly DWG contains binary records, rather than any readable text fragments; also new versions tend to use compact forms of the fragments, readable only via CAD parsing engine. Also DWG references external resources instead of being filled with internal content. References are often SHX and TTF fonts, raster images, underlay references, xref DWGs, plot style table (CTB, STB forms); additional fragments include: linetype tables, custom object enabling tables too. The size of a DWG file can reach up to hundreds of MB for complicated civil or plant constructions, BIM-derived, xref-rich, and rasters.

According to Autodesk, DWG media type is image/vnd.dwg; additionally supported media types are: application/acad, application/x-acad, application/autocad_dwg, image/x-dwg, application/dwg (older Autodesk platforms). The whole DWG specification by Autodesk itself remains closed, that means there is no full support possible via 3rd party software tools, which could parse DWG; the alternative is RealDWG, or ODA libraries, or open sourced part implementation, like LibreDWG.

How to convert .DWG files

DXF format can serve as a standard editable interchange target from DWG owing to better documentation and compatibility of DXF with CAD, CAM, GIS, and Vector graphics systems. Batch export from DWG format can be achieved through command such as ODAFileConverter ./input ./output ACAD2018 DXF 0 1 "*.dwg", where GNU LibreDWG can process batch exports using: dwg2dxf -o drawing.dxf drawing.dwg,Copy in case when it concerns appropriate DWGs, however changes might appear regarding custom objects, parameters constraint, annotative scaling, layouts, 3D elements.

Earlier DWG versions are needed whenever recipient uses older CAD software to which DWGs of AC1032/AutoCAD 2018 can not work at all. Using Save As from AutoCAD, DWG convert tool in DWG TrueView, ODA file converter, BricsCAD/DraftSight can achieve required DWG, for example ODAFileConverter ./input ./output ACAD2013 DWG 0 1 "*.dwg" gives ACAD2013 DWG export output.

PDF serves as standard interchange format for review purposes and printed sheets owing to preserving sheets, lineweights and annotations for a non-editing party, and QCAD Professional offers command: dwg2pdf -o drawing.pdf drawing.dwg. The use of DWF and DWFx is limited strictly only to creating markups of DWG by Autodesk review set program. Other format, namely SVG, EPS, PNG and JPEG, which might be suitable for websites' and PowerPoint-like presentations, can reduce some complexities like scales, layers of drawings, text and lineweights in drawings, and can mix up spaces: model and paper. IFC format can be applied only in the presence of BIM objects; STEP/IGES/SAT formats deliver 3D solid and surface representations of a 3D part.

Saving original drawings before the process of their batch translation must be obligatory because of silent font modifications, links/xrefs and other factors.

Common problems and fixes

"Drawing File is not valid" in AutoCAD may refer to corrupting of the DWG database, not real DWG file or truncation in download/e-mail attachments, a third-party translator generating erroneous results, etc. Check the correct file start, usually with AC1027/AC1032 for a DWG version number, try to repair the DWG file manually with AutoCAD RECOVER or DWG TrueView and/or try some different ODA File Converter-based tools; if unsuccessful with multiple tools ask the sender to send another exported/origin file.

"Drawing file is created by an incompatible version": the CAD is old to work with the current DWG - the case when an obsolete CAD program tries to open AC1032 file (used by AutoCAD 2018 - 2026). Save your DWG in the desired version like AutoCAD 2013/2010 using AutoCAD SAVEAS/DWG TrueView DWG Convert/ODA File Converter to convert your DWG to the older DWG/DXF version.

Warnings "Non Autodesk DWG" or TrustedDWG: they signalize about opening an external application file which can be absolutely fine. Use AUDIT to verify integrity of drawings and also compare printed/draft sheets; check dimensions/coordinates/blocks/custom objects as well if any contractual fidelity is needed.

"You have one or more SHX or TTF fonts referenced in this drawing which cannot be loaded". It refers to substituting of text symbols/linetypes and dimensions - just load all missing SHX/TTF fonts or redefine text fonts mapping and then reverify the resulting plot/drawing.

"Proxy Information" warning box refers to a file containing custom drawing objects generated by Autodesk products - usually AutoCAD Architecture/Civil 3D /Plant 3D/mechanical add-on and similar programs. Load required object enabler plug-ins or open file by corresponding software.

Missing xrefs/underlays/raster images or/and linetypes/CTB/STB Plot Style Tables lead to incomplete view/resulting plot - the solution - request complete transmission in ETRANSMIT feature and if possible avoid opening the files in older CAD program.

Slow loading/crashes often happen because of high number of regapps or dense hatched entities or images or even point cloud, too nested xref; you have to perform AUDIT, PURGE and especially - "-PURGE REGAPPs"; use OVERKILL utility and xrefs cleanup. A DWG may be opened read-only because of permission problems, network or cloud synching or existence of stale .dwl/.dwl2 lock files after exclusion the chance for another users to have the file open.

Security considerations

The DWG file format is not a macro type of document as found in the MS Office suite and opening this file format will not trigger macros to execute automatically in general. The following AutoLISP files, VBA / DVB, .NET programming, scripts, plugins and ARX and DBX programming language could run when loaded in the specified support directories in a CAD environment; hence one should avoid opening unknown CAD Drawings in unprotected AutoCAD, DWG TrueView software, BricsCAD or DraftSight or open it in an isolated environment inside a virtualized machine environment as this Drawing may contain a malware or vulnerability for example parsing memory corruption bugs or a security bug involving malicious CAD drawings. The drawing may contain OLE objects, links to websites and files and custom proxy, fields, external references (xrefs) and image file links. Review the authoring details including username, template names, Layer names and Block Names in addition to Comments, Geographical location and Coordinate System and xrefs paths and the rest paths and layout Titles and revision information as well as frozen Layers.

History and versions

DWG format was the initial drawing database of AutoCAD which was released by Autodesk company in December 1982 on personal computer-based CAD drafting program. As AutoCAD file format, .dwg extension stands for the word drawing and became the unofficially recognized norm due to the AutoCAD dominant role in exchange of editable 2D CAD in domains of architecture, engineering, construction and manufacturing.

For a number of years in the early '90s AC1009 DWG was the base format and corresponds to AutoCAD R11/R12. Many companies use R12 DWG/ DXF as many other programs that can convert CAD formats support this one. Autodesk company has developed new databases generation according to their AutoCAD software releases starting from the 1990s' R13 and R14 formats and following formats have emerged, as: AC1015/AutoCAD 2000; AutoCAD 2004; 2007; 2010; 2013; and 2018 family formats and others.

The latest format family - AC1032 - or AutoCAD 2018 is current for the AutoCAD releases from 2018 until 2026 and provides increased compatibility between these releases. RealDWG license is provided to developers of software by Autodesk and they use a feature of TrustedDWG alerts for files created either by themselves (Autodesk company) or by realDWG-based programs. Open Design Alliance has founded its organization in the end of '90s, it used to be called as the OpenDWG Alliance and provided DWG technology for reading and writing that many non-Autodesk CAD software uses.

Related formats

While Autodesk DXF, known as Drawing Exchange Format, has less efficient structure when compared to Autodesk DWG, a greater transparency enables it to be imported/exported using other CAD, CAM, GIS or vector-based software packages.

.DWF, or Design Web Format, is another publishing format developed by Autodesk that can be used for plotting drawings along with additional markup data and their distribution while .DWG file should be kept as a master file which will enable making subsequent modifications and edits easily. Bentley MicroStation DGN is usually more compatible for such project if standards/cells/levels are made using MicroStation.

Autodesk Revit .RVT is another example of format that has to be used if working with building information model and needs to be kept in order not to lose parametric properties. DWG files contain only geometrical drawing/model without any information about building process.

.STEP and .IGES have to be used for solid/mesh and surfaces modeling while .DWG will have much better results when working with 2D drafting/AutoCAD layouts. If using .SKP (file type) for working with concepts - then it is easier way since DWG is less convenient for 3D concept modeling.