If you have backed up via certain tools, the backup files can be extracted easily and restored to a new device. But if you simply want to transfer files stored in PDF Reader to another device, you could try the following steps:
- Switch to the Document tab for the file list
- Select files and move them to one single folder
- Tap “Edit” on the top right corner
- Select the folder and choose “Zip” to compress the folder into a zip file
Transfer to Desktop via iTunes USB
You could transfer the zip file from your iOS device to PC/Mac via iTunes USB first and then restore it to a new device. Or you could choose to sync the zip file to another device through Kdan Cloud or other cloud storage services.
Note: For devices running iOS 12 and later, PDF Reader Premium and PDF Connoisseur as well as other 32-bit apps can not be opened. You can access your files located in these two apps via iTunes if you connect your device to PC/Mac with a USB cable.