Are you looking for older version of SketchBook? Do you have a machine that can't be updated, so its specs aren't compatible with the latest version of SketchBook? Though the older versions don't have the speed, latest tools, and all the other bells and whistles, they might work on your device or machine, if you can find them.
If you're having issues with an older version of SketchBook, please check the SketchBook Forum for solutions.
If you are on a mobile device and the app is no longer listed on the App stores, you can only download an older mobile version, if you originally downloaded it, while it was still on the store.
Read this article, How to downgrade to an older version of apps on Android, for instructions.
On your device, in iTunes, tap Purchased (found in the toolbar at the bottom of your screen). This will list all purchased and free apps.
For how to recover old drawings from older versions of SketchBook, please see this article on the SketchBook Forum.
If you are trying to update to 4.0 and have a 32-bit device, a message appears letting you know the app isn't compatible with your device. In this case, the version you were using yesterday will be the same version you will have today (since an update wasn't possible).
If you want to reinstall an older version of SketchBook, which is not a subscription version (anything before version 3.0):
The links below are for older versions of SketchBook. However, to download and run them, you need a serial number and product key from a purchased version of SketchBook prior to 2015.
If you have found a different version of SketchBook and are thinking of using it, here some important articles to read. They will instruct you on what you might need to do to ensure you don't lose or damage your files.
If you aren't sure what version you have installed, check out What version of Autodesk SketchBook am I running