Will uninstalling an app delete the documents I made with it?
Short answer: No. Uninstall only collects the app and its own files in your Library, not documents in your folders. Check the list for app-stored data and untick what you want to keep.
No. Uninstall only collects the app and files in your Library whose names clearly belong to that app. Documents you saved in your own folders — Documents, Desktop, iCloud Drive and so on — aren't included.
One thing to check: some apps keep their own data inside their support or container folder. Look over the list before confirming, and untick anything you want to keep.