You can use the Notes app to scan documents such as registration papers and save them as a pdf. If decide to use this route, please make sure you are in a well lit area without shadows.
1. Open Notes and select a note or create a new one.
2. Tap the Camera button , then tap Scan Documents .
3. Place your document in view of the camera.
4. If your device is in Auto mode, your document will automatically scan. If you need to manually capture a scan, tap the Shutter button or one of the Volume buttons. Then drag the corners to adjust the scan to fit the page, then tap Keep Scan.
5. Tap Save or add additional scans to the document.
Source: support.apple.com