Best practice is, you need to upgrade your Kentico 9 version into Kentico 12 version and export Page Types from source to Target Kentico 12 version.
Go through the Kentico documentation for upgrade 9 to 10, 10-11 and 11-12
Workaround is ,
Option 1: export Page Types from Kentico 9 Project and Import into Kentico 12 project. This may work with some warnings while importing.
In case this gives an error go for option 2.
- Export Page Type from Kentico 9 Project
- Unzip the export file and change the version in all XML files from 9.0 to 12.0 the version number in the first line of each XML file.
- Zip this back updated folder
- Import this updated zip into Kentico 12 Project.
One of these options may possibly work for you.