https://www.theverge.com/how-to/673060/how-to-scan-documents-using-your-iphone
Please read more at the above link
The process of scanning a document is similar in both Notes and Files. To get started in Notes, open or create a note, then tap the paperclip icon at the bottom, then Scan Documents. In Files, tap the three dots (top right), then Scan Documents.
This gets you into the scanning interface. By default, you’ll be in auto mode — frame the document in the camera viewfinder, and when it’s lined up, a picture is automatically taken. Line up the next page, and after a moment, another capture is made.
Tap Auto (top right) to switch to manual mode, which lets you take each snap using the shutter button manually. The Auto button changes to read Manual, and you can tap it again to switch back to automatic mode.
You’ll see a couple of icons at the top. The lightning bolt lets you control the flash, while the three circles lets you switch between Color, Grayscale, Black & White, and Photo for the scanning mode.
When all the documents and pages have been captured, tap Save. In Notes, the pages you’ve scanned are then added to the current note, and in Files the pages are saved together as a PDF file (you may be asked where you want to save your file).