Evernote Scannable for iOS devices:
In the App Store, download Evernote Scannable. (You can also download and follow a similar process with another scanning app that produces high-quality PDFs.) Open Scannable. Click the three dots > Settings > File Type > PDF. Then, click the back arrow > Done. Hold your phone above each page. The app will scan each page automatically as soon as it finds it. When you've scanned every page, click the check mark. Review your scans for legibility. Make sure all pages are in one PDF. Name your file by tapping the file name next to the PDF icon. Click Send. Then, click Mail to email the scans to yourself or click Share > Save to Files or Dropbox (or another cloud service). You may need to scroll to find all the "Save to.." options on your phone.

Genius Scan for Android devices:
In the Play Store, download Genius Scan. (You can also download and follow a similar process with another scanning app that produces high-quality PDFs.) Open Genius Scan. Select the camera icon on the main screen. If you’re scanning multiple pages, tap the image icon in the top right corner of the screen to switch to batch mode. Hold your phone above each page and click the spinning circle. Repeat for each page. The number in the circle will track how many pages you’ve scanned to the document. Click the check mark when you’ve scanned all your pages. Make sure all your pages are in one document. Name your document by tapping the file name at the top of your screen. Review your scans for legibility. Select your document, click the Share icon. Make sure the Format is set to PDF. Then, click Mail to send it to yourself, click Device Memory to save it on your phone, or click Google Drive or Dropbox (or another storage option) to save it to the cloud.