Is a phone scan good enough for official documents?

For online submissions, yes — portals are typically checking legibility and file size, both of which a phone scan handles well. The two things that get rejections are shadows across the text and a crop that clips an edge of the page, and both are avoidable with side lighting and a little margin.

How do I make a scanned PDF searchable?

Run OCR on it. It reads the image, works out where the characters are, and writes an invisible text layer behind the picture. The page looks unchanged and search, copy and screen readers all start working.

My scan came out as several separate files. How do I combine them?

Merge them into one PDF, keeping the page order. Better still, next time keep shooting into the same scan session — every built-in scanner lets you add pages before you save.

Why is my scanned PDF 30 MB?

Because each page is a full-resolution photograph. Colour scanning at high DPI is the default on most scan modes, and it is far more detail than a document needs. Grayscale and compression together usually take a scan of that size to under 3 MB with no loss of legibility.

how to scan a document with my phone

How to Scan a Document With Your Phone

A photo of a page and a scan of a page are different things. The difference is edge detection, perspective correction and contrast, and both iOS and Android do all three for free.

Use the scanner, not the camera

A camera photo of a document arrives skewed, with the desk in frame, uneven lighting across the page and grey-ish paper. A scan mode finds the four corners of the sheet, flattens the perspective so the page is rectangular, crops everything outside it and pushes the paper to white and the ink to black. The output is a PDF, not a photo, and it is dramatically smaller and more legible.

Both platforms have this built in and neither advertises it well.

iPhone: Notes → new note → camera icon → Scan Documents. Or Files → ⋯ → Scan Documents to save straight into a folder as a PDF.
Android: Google Drive → + → Scan. Saves as a PDF to the folder you choose.
Samsung: The camera app often detects a document and offers a scan shortcut on screen; Samsung Notes also exports to PDF.
Multi-page: All of them let you keep shooting pages into the same document. Do that rather than making one PDF per page and merging afterwards.

The four things that decide whether it looks good

Scan quality is almost entirely about the two seconds before you tap the shutter.

Contrast under the page: Put white paper on a dark surface. Edge detection works by finding the boundary, and white-on-white gives it nothing to find.
Light from the side: Overhead light plus a phone held overhead means your own shadow lands on the page. Face a window, or put a lamp off to one side.
Flash off: The flash produces a hot white blowout in the middle and dark corners. It makes almost every scan worse.
Fill the frame: Hold the phone parallel to the page and get close enough that the sheet nearly fills the viewfinder. Pixels spent on the desk are pixels not spent on the text.

What to do with the file afterwards

What comes out is a colour PDF, typically one to three megabytes a page. That is fine to keep and usually too big to upload, so there are normally two more steps.

First, if it is black text on white paper, convert it to grayscale. There is no colour information in it worth carrying, and it removes 20–40% before any compression happens. Then compress, which on a scan routinely takes off another 50–90%.

Second, consider OCR. A scan is a picture of words — you cannot search it, select from it, or have a screen reader read it aloud. OCR adds an invisible text layer underneath the image, so the page looks identical but Ctrl+F starts working. That matters more than it sounds: an unsearchable archive of scans is very close to an archive you cannot use.

When to use a real scanner instead

Three cases. Bound books, where the page curves away from the spine and perspective correction cannot flatten a curve. Anything you need at genuine high resolution — artwork, photographs, documents going to print. And bulk: forty pages through a sheet feeder takes two minutes and forty pages by phone takes considerably longer, however good the result.

For everything else — a signed form, a receipt, an ID, a certificate for an upload — the phone is not a compromise. It is faster and the file is smaller.