You do not need a flatbed scanner to scan a document. A phone camera does a good job for one or two pages, and a scanner or all-in-one printer is the better choice for a stack of pages.
Method 1: iPhone Notes app
Open the Notes app and start a new note.
Tap the camera icon, then select Scan Documents.
Hold the phone over the page. It detects the edges automatically. Tap the shutter button to capture.
Drag the corners to fix the edges if needed, then tap Keep Scan. Tap Save when you are done.
To share it, tap the Share button in the note and choose Save to Files or Mail. The scan is saved as a PDF.
Method 2: Android Google Drive app
Open the Google Drive app.
Tap the + New button, then select Scan.
Point the camera at the page and tap the shutter button. Tap the checkmark to keep the capture.
Tap the + button to add more pages, then tap Save. Choose a name and a Drive folder, and the scan is saved as a PDF.
Method 3: Windows Scan app
Place the page face down on the scanner glass, or in the document feeder.
Open the Start menu, search for Scan, and open the Windows Scan app. If it is not installed, get Windows Scan free from the Microsoft Store.
Pick your scanner from the Scanner list, and choose Flatbed or Feeder under Source.
Choose a file type. For a document you plan to email, JPEG works well. For a photo, JPEG or PNG.
Select Scan. The file saves to the Pictures, then Scans folder, unless you pick another location.
Windows Scan does not save directly as a PDF. It offers JPEG, PNG, TIFF, and Bitmap only. To make a PDF from a scan, open the scanned image and print it to Microsoft Print to PDF, or scan with your phone instead, which saves as PDF by default.
Tips for a clean scan
Scan on a plain background with good light, and hold the phone steady. For a phone scan, lay the page flat and avoid shadows from your hands. For a stack of pages, the document feeder on a printer is much faster than the flatbed, one page at a time.
Common questions
Can I scan a document without a scanner? Yes. The iPhone Notes app and the Android Google Drive app both scan with the phone camera and save the result as a PDF.
Where do Windows Scan files go? To the Scans folder inside Pictures in your user folder, unless you pick a different save location before scanning.
Why does Windows Scan have no PDF option? The app only offers image formats: JPEG, PNG, TIFF, and Bitmap. Print the scanned image to Microsoft Print to PDF to turn it into a PDF, or scan with your phone instead.