With iOS 11 and later, you can scan a document with the Notes app.
- Open the Notes app.
- Create a new note.
- Tap the camera symbol at the top of the keyboard and choose "Scan documents" from the menu.
- Place your document in view of the phone's camera.
- Tap the capture button if it doesn't scan automatically.
Once captured, you can drag the corners to fit the page. You can then add pages or save when done. Then click the share icon to email or text the document to yourself or someone else.
Android (Google Drive)
- Open the Google Drive app.
- In the bottom right, tap the plus botton to add.
- Tap the camera icon.
- Take a photograph of the document you'd like to scan.
- Adjust by tapping the crop icon, re-scan, or add additional pages.
- Tap done.
Other options (Adobe Scan)
Adobe Scan is a free app available on iphone and Android for free. This app does auto-cropping, image cleaning, high resolution scans, and can automatically store it in Adobe Document Cloud.