With PlayScore all processing and storage takes place on your device alone. Your documents are stored on your device only and are never sent anywhere unless you explicitly share them. There is no central server where documents are stored and no information from your device is ever shared with us.
This is good for speed, for copyright protection and for privacy, but it does mean that PlayScore does not sync your documents over multiple devices. It also means that if you uninstall PlayScore or reset your device to factory settings your PlayScore documents will be lost.
Most documents can easily be recreated from the original PDF or paper music. But if you want to keep a backup you can use any storage service like Google Drive, Dropbox and iCloud.
Backing up Documents
You can do this individually or in bulk from the Documents screen. First tap Select, and then tap in turn the documents you want to store. Now tap the Export symbol and choose to share As Document. From there you can choose any installed storage service.