As you have reset the device and the files were saved on iCloud, then there is nothing that can be done from our end. You will need to check with the iCloud support team if the files does not appear on that account.
If you were using the Adobe Acrobat Reader, you can save the files either locally or on the Document Cloud.
You may try checking the files on Document Cloud. Open this link and sign in using the same credentials that you used for Reader application on the device. Once you are signed in, go to Files and check if you can find the files there in the list.
The files saved locally on the device gets removed if you uninstall the application. If you have not taken any backup of those files, it is not possible to retrieve them now.
Hope the information helps.
Let us know if you have any questions or if you are referring to something else.