Two cases where this helps
In the first, the document already exists digitally (PDF, Word, Excel, slides) but has to be delivered as a scan. In the second, you only have a paper sheet and can photograph it.
Either way, Let's Scan turns the source into a PDF with the signs of a real scan: slight skew, grain, soft light and paper tone.
How to photograph a sheet well
Lay the sheet on a flat dark surface and shoot from above in even light, without your phone's shadow. The whole page should fit in the frame. iPhone HEIC photos work too.
After uploading, switch to B/W for a “straight off the scanner” copy and raise contrast a little to lighten the background.
No install, no cloud
There is nothing to install: it runs in your browser on desktop and mobile. Files are processed on your device and are never uploaded.