How does a scan differ from a text document?

A scan is a page taken by a camera or a scanner. At first it is a picture. The letters are visible, but a program may not know them as writing. Text recognition tries to pull writing out of that picture.

In a text document you can select the letters with a finger or a mouse. If you cannot, the page is still a picture. Recognition can misread names and numbers, so the result needs a look.