Why your scanned PDF is so big, and how to shrink it
A one-page typed document can be 50 KB. A one-page phone scan of the same page can be 3 MB. The difference is what is inside the file.
Text versus pictures
A typed PDF stores letters, which take very little space. A scan stores a photo of the page, with millions of tiny dots of colour. More detail and more colour means a bigger file.
What makes a scan bigger
- High resolution. Phone cameras capture far more detail than a form needs.
- Colour. A black-and-white page is much smaller than a colour one.
- Many pages. Each page adds its own image.
- Shadows and paper texture. Noise is hard to compress.
How to shrink it
- Open Compress PDF and choose your file.
- Pick the size limit your form allows.
- Download the smaller copy.
In our own tests, a test PDF full of photos went from about 1.8 MB to about 340 KB. Your results depend on the file.
Scan smarter next time
- Use a scanner app set to black and white or greyscale for text pages.
- Choose around 150 to 200 dpi, which is plenty for reading.
- Lay the page flat in even light so there are no shadows.
One thing to know
When a scan has to be shrunk a lot, the tool may turn the pages into images. The page looks the same but the text can no longer be selected or searched. The tool tells you when this happens.