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1. SAC 2024 backward compatibility broken

Since Civil 3D 2024, people suddenly found that custom Sub assemblies saved by Sub Assembly Composer (SAC) 2024 are NOT compatible with SAC 2023, 2022 or lower any more.

The .PKT  file compatibility broken since SAC 2024 is NOT explicitly announced by Autodesk.  The situation may be annoying when someone has accidentally upgrade old PKT file without backup  and  now have to recreate it in SAC 2022.

The reason for this error message is: 

Since Civil 3D 2024, the .dll file inside pkt file has been removed and a new .cdmd file has been added.

2. Make SAC 2024 pkt file compatible with SAC 2022

To fix the "invalid .pkt file" error and make the 2024 pkt file compatible with SAC 2022, do the following:

1. Change 2024 pkt file extension to zip, extract all to a new folder

2. Explore the folder created in (1), change the extension of .cdmd file to .dll

3. Edit the file [Content_Types].xml,  replace "cdmd" with "dll"

4. Select all file in folder and create a zip file.  Rename .zip extension to .pkt

3. Remarks

• Since SAC 2023, Autodesk has introduced Auxiliary Curve. Though this feature is not supported by SAC 2022 and below,  the 2023 .pkt file with Auxiliary Curve still can be opened in SAC 2022 with some error messages. 

• Please note that this solution may not work if your pkt file is complex, but it is simple and worth a try.

Civil 3D 2025 continues to break the pkt file backward compability

A pkt file saved by SAC 2025 cannot be opened in SAC 2024.

We will soon show you a solution for this...