Scanning with a phone camera turns paper into a PDF without a scanner: open this page on the phone, photograph each page, and download the set as a single document. The captures stay on the device — they are held in the browser tab and assembled there, so a photographed passport, contract or medical letter is never uploaded to anyone's server, which is a meaningful difference from most scanning apps. Quality depends almost entirely on how the photographs are taken rather than on any processing afterwards: even, indirect light, the phone held parallel to the page rather than at an angle, and the page filling the frame will produce something legible enough for any official purpose. Shadows are the usual culprit when a scan comes out unusable, and the phone's own shadow is the one people forget about.
Light is most of the result
Diffuse indirect light is what you want: near a window on an overcast day, or under general room lighting rather than a single spotlight. Direct sun produces harsh shadows and blown-out highlights; a desk lamp produces a bright patch and dark corners.
Watch for your own shadow and the phone's. Holding the camera directly above a page under a ceiling light frequently puts the phone's shadow across the middle of the shot. Move so the light comes past you rather than from behind you.
Angle, framing and focus
Hold the phone parallel to the page rather than tilted. A tilted shot gives keystoned pages — narrower at the top than the bottom — which look wrong in a document and can make automatic processing fail later.
Fill the frame with the page, leaving a small margin, so the resolution is spent on the document rather than the table. Tap to focus before capturing, especially in dimmer light, and check the smallest text on screen before moving on: a blurred page is much easier to retake now than after you have put the paper away.
Assembling the document
Capture in order and the pages arrive in order. If you photograph out of sequence, fix it before downloading — it is far quicker than reordering the finished PDF.
The result is a set of photographs in a PDF wrapper, which means the text is not selectable and the file can be large. Compressing afterwards helps with size; OCR is what adds a searchable text layer if the document needs to be searched or read by a screen reader.