That depends on where exactly you have saved those documents? Was it saved on Document Cloud?
You may confirm couple of things to understand the issue in better manner.
I assume you are referring to the Acrobat Reader DC mobile application?
Also, If you are "Signing In" in the application using the same email address that you have used before, then only you can access the files saved on "Document Cloud". Are you using the correct email address?
If you did uninstall the application and installed again then data saved in "Local" will be gone.