uppose you want to make backup copies of your books and documents from other places, such as Kindle or Google.
You might want to do that just for safety, or you might want to put those books on a smartphone or tablet.
You would do the latter to be able to access those books away from Wi-Fi, and/or to avoid using expensive data access.
In all likelihood, backup to a tablet or smartphone may very well require additional storage space in the form of an SD card.
In backing up, It is easy enough to back up purchased books from Amazon or Google. You just download them to your device. In Google you need to identify such books in order to do so.
However, you may have books and and documents you have obtained elsewhere. You might have uploaded these documents to Amazon or Google. In Amazon you email Pdfs to your Kindle account as an attachment, using the word Convert in the subject line.. In Google Play Books you upload them from your My Books screen
Amazon will download them to your device as with books.
In the case of Google, this presents a challenge. it might be better to have saved such documents to Google Drive or Dropbox. However it is very convenient to save them to My Books in Google Play Books.
If that is where your documents are, to retrieve them, requires a utility from Google. This utility is called Takeout. Tap or click for it here.
This utility will archive the data you have in Google. You got the ability to select Google Play Books in particular. Eventually you'll receive an archive. You will be notified in your email when it is ready to download.
If you need an app to read these files, the Overdrive Library app will work for most.That is the app that accesses books from your local library. Tap or Click for it here.