You do not need a scanner, and you do not need to install anything. A phone camera and a few minutes of care produce a document that is perfectly acceptable to most offices.
Lighting does most of the work. Daylight from a window, with your own shadow out of the way, beats a ceiling light directly overhead every time. The single most common reason a scan gets rejected is a dark band across the page from the person taking the photo.
Shoot straight down. Photographing at an angle makes the page a trapezoid rather than a rectangle, which looks careless and can make the text harder to read along the far edge. Getting the camera parallel to the paper costs nothing.
Crop before converting, not after. Cutting away the desk reduces the file size considerably and makes the finished PDF look like a document rather than a snapshot of one.
Put the page on a plain dark surface in even light, and hold the phone directly above it so the edges are square. Avoid your own shadow across the page and fill the frame so the text is as large as possible. A sharp, straight photo is the difference between a document that reads clearly and one that is rejected.
Trim any background with Crop & rotate, then build the PDF. The pages are pictures, so the PDF is not searchable. If you need the words as text, run the pages through Image to text afterwards.
For most purposes yes, provided the text is sharp and the whole page is in frame. Some institutions insist on a real scanner, and they will say so.
Yes, add the photos in order and they become one document.
No. The PDF is assembled on your own device.
No. The pages are pictures. Use Image to text if you need the words as editable text.