You send a drawing out and get one line back: it will not open here. That is the moment you have to save a CAD file to an older version. The tool for it ships with AutoCAD, needs nothing installed, and takes seconds once you know where it lives.
This article follows the order a drafter actually needs. Why the older seat gives up, how to save one file down, how to set the format once and forget it, how to convert a whole folder, and what the drawing quietly loses on the way. For the full drafting and documentation workflow, see the AutoCAD for Construction course.
Why an older seat cannot open a newer DWG file
The DWG file format does not change every year. It changes every few years, and each change creates a new milestone.
A newer release always reads an older milestone. The other direction fails, because the old release has never heard of object types invented after it shipped. That is how the format is designed, not a fault on the machine.
The practical consequence is short. The sender has to step the file down before sending, because the recipient can do nothing about it on their own machine.
The quick way: save a drawing to a previous release with SAVEAS
Autodesk sets out four steps on the To Save a Drawing to a Previous Release Format page.
Type SAVEAS and press Enter. The Save Drawing As dialog opens. Give the file a different name in File name. Open Files of type and pick the milestone you need, for example AutoCAD 2007/LT2007 Drawing (*.dwg). Click Save.
| Number | Box | What it does |
|---|---|---|
| 1 | File name | The file name. No extension needed, the program adds one to match the format |
| 2 | Files of type | The output format. This is the box that decides everything, and the one most often skipped |
| 3 | Save | Writes the file. On a name clash it asks once before overwriting |
One detail sits right in the About Saving Drawings to Previous Drawing File Formats page — "be sure to assign a different name to avoid overwriting the current drawing". Stepping down is a one-way loss. Overwriting the original throws away the complete copy with your own hand.
If you did overwrite it, one way back remains. The .bak file beside the drawing is the copy from before that save, and renaming it to .dwg opens it again.
Sixteen entries in the Files of type list
Click Files of type and the list drops down with exactly sixteen entries. They fall into three clear groups.
| Group | What it holds | When to use it |
|---|---|---|
| Seven DWG milestones | From AutoCAD 2018 down to AutoCAD R14/LT98/LT97 | The recipient runs AutoCAD, just an older release |
| Two other extensions | .dws is a standards file for auditing, .dwt is a template | Nothing to do with stepping a release down |
| Seven DXF milestones | From AutoCAD 2018 down to AutoCAD R12/LT2 | The recipient runs other software that cannot read DWG |
The top line is preselected, and it writes the format named 2018.
Set a default format so you stop choosing every time
Every office has one seat it must accommodate. Rather than remembering to change the box each time, set it once.
Type OPTIONS, go to the Open and Save tab, and open Save as in the File Save group. The Open and Save Tab page states the reach of that box — "The file format selected for this option becomes the default format for saving drawings".
It governs SAVE, SAVEAS, QSAVE and WBLOCK alike. From then on every Ctrl+S writes straight to the milestone you picked.
A lookup table of DWG file format versions
Two numbers get mixed up constantly. The release name is a product year, while the file format is a different milestone altogether.
| Code in the file | Format milestone | Releases that share it |
|---|---|---|
AC1014 | R14 | R14, LT98, LT97 |
AC1015 | AutoCAD 2000 | 2000, 2000i, 2002 |
AC1018 | AutoCAD 2004 | 2004, 2005, 2006 |
AC1021 | AutoCAD 2007 | 2007, 2008, 2009 |
AC1024 | AutoCAD 2010 | 2010, 2011, 2012 |
AC1027 | AutoCAD 2013 | 2013 through 2017 |
AC1032 | AutoCAD 2018 | 2018 through 2027 |
These codes come from the $ACADVER entry in the vendor's own DXF Reference. The first six characters of any DWG file are that code, readable in a plain text editor.
The table also explains why most handovers go through untouched. Every release from 2018 to 2027 shares one milestone, so files pass back and forth with nothing to change. Only a recipient on 2017 or earlier forces a step down.
There is a third number as well. The ACADVER variable returns the product number, 26.0 on the 2027 release, and its ACADVER page notes that it differs from the $ACADVER header of a DXF file. Three numbers, one seat.
Batch convert DWG files with DWGCONVERT
Saving one file down is fine for a couple of drawings. A package of several dozen needs another road, and that road is already inside AutoCAD.
Type DWGCONVERT. The DWG Convert dialog opens. Click Add File to bring drawings in, or drag them onto the list. Pick a setup under Select a Conversion Setup, then click Convert.
The default setup is called Standard. Click Conversion Setups and then Modify to reach the detail dialog, and that is the part worth reading closely.
File Format sets the milestone to step down to. The Conversion Package Type group chooses how the output is delivered, with three options whose consequences differ sharply.
| Package type | Result | Note |
|---|---|---|
In-place (Overwrite Files) | Writes over the original files | Only this type enables Create backup (*.bak) Files |
Folder (Set of Files) | New files land in a separate folder | The safest choice, originals untouched |
Zip (*.zip) | One compressed package | Easy to send, but carries a file name trap |
The trap sits in the vendor documentation itself. The Modify Conversion Setup page says the archive is written as UTF-8, and that "the names will not display correctly if you use ZIP utilities that do not support UTF-8 format ZIP files". Any team whose file names carry accented characters will hit this. Autodesk suggests an extractor that understands UTF-8, such as 7-Zip.
Three more boxes in that dialog earn their keep. Check and Fix Errors audits structure and repairs it before converting. Purge Drawings clears unused definitions so files come out lighter. Set Default Plotter to None strips your own plotter out of what you send.
Every conversion run writes a log file. The About Batch Conversion page states its purpose exactly — "a log file lists the information that was lost or changed". Plenty of guides tell readers to ignore that file. That advice is backwards, because it is the list of everything the drawing just dropped.
Stepping releases down repeats many times over a project. The file list saves as a .bcl file through Save List, and Open List brings the whole list back next time.
What a drawing loses on the way down
This is the half the popular guides leave blank, and the half that decides whether what you send is usable.
| Down to | Lost or changed |
|---|---|
2007 | Multileaders turn into objects the old seat cannot edit, and DGN underlays do not display |
2004 | Dynamic block geometry separates from its parameters and stops updating on reopen |
2000 | File size can grow, and encryption and digital signatures are not preserved |
R14 | Hyperlinks change form, and some dimension styles may lose their original colour |
R12 DXF | Extra layouts are gone, object names are cut to 32 characters, spaces become underscores |
The first two rows matter most to construction documents. The About Converting to Previous Drawing File Formats page states plainly that at the 2007 milestone "Multileaders display as proxy objects in releases prior to AutoCAD 2008". Your whole annotation set arrives on the recipient's machine as objects they cannot edit.
Annotative text carries a trap of its own. With Maintain Visual Fidelity for Annotative Objects ticked, each annotation scale is split onto a new layer named after the original with a number appended. The drawing therefore opens on the far end with a crop of unfamiliar layers. Layer housekeeping is covered in layers in AutoCAD.
That box only bites at the 2007 milestone and earlier, exactly as the Open and Save page notes. Step down to 2010 or 2013 and it is not a concern.
One more limit is rarely mentioned. A drawing written to the 2007 milestone or earlier cannot hold an object larger than 256 MB. Heavy three-dimensional work and point clouds reach that ceiling first.
Dynamic block definitions deserve a check after every step down, along the lines set out in blocks in AutoCAD. Reopening the file you just wrote and looking through it is a habit worth keeping before you press send.
When to use DXF instead of DWG
The seven DXF milestones serve an entirely different purpose. DXF is a text-based interchange format published by Autodesk, so any vendor can write a reader for it.
Reach for DXF when the recipient runs software that cannot read DWG, such as machine tools, analysis packages or mapping software. The AutoCAD R12/LT2 DXF entry is the lowest rung, and it is still the usual choice for a cutting shop.
Avoid DXF when both ends run AutoCAD. A DXF file is much heavier than the DWG holding the same content, and several AutoCAD-specific objects break apart in the conversion.
The R12 DXF rung also severs the link between dimensions and geometry. After reopening, the numbers no longer follow the lines they measure.
Anyone stepping releases down in bulk can set the FILEDIA variable to 0. SAVEAS then asks at the command line instead of opening a dialog, which makes it scriptable. The prompts are listed on the SAVEAS Command Prompts page.
How to open a newer DWG file on an older seat
The reverse situation is just as common. A file arrives, it will not open, and the sender has gone quiet.
The first road is to ask the sender to save it down. This is the cleanest one, because a step down performed on a full seat loses the least.
The second road is DWG TrueView, the free drawing viewer from Autodesk. It carries the same DWG Convert feature found inside AutoCAD, so you can step files down without a licence. The vendor documentation notes one limit: parametric constraints authored from the 2010 release onward do not display there.
The third road is moving up a release. That is the only permanent fix, since a newer seat reads every older milestone. The command set and the way of working change little, and what AutoCAD is runs through what to know before the move.
One closing caution. Keep real project files away from online conversion sites. A construction drawing is a legal document, and uploading it to an unknown server is not a risk worth taking.
Frequently asked questions
Does it damage the drawing to save a CAD file to an older version?
It does not corrupt anything, but it does lose things. The program strips or converts objects the older milestone never knew. The safe habit is to keep the master in the current format and send only the stepped-down copy.
Which milestone is safe to choose?
Ask which release the recipient runs, then read the table above. The deeper you go the more you lose, so pick the milestone that just clears their seat rather than dropping to R14.
Why does a file saved to 2007 open with a crop of unfamiliar layers?
That is the signature of Maintain Visual Fidelity for Annotative Objects being on. Each annotation scale is split onto its own layer, named after the original layer with a number appended.
What do I use if there is no AutoCAD on my machine?
DWG TrueView from Autodesk. Its DWG Convert feature does the same job as DWGCONVERT inside AutoCAD.
Is the log file written after a conversion worth keeping?
Read it once before the package goes out. It is the list of what was lost or changed during that conversion run.