How to compress a PDF to a specific size
Upload forms and email systems often say "PDF must be under 200 KB" without telling you how to get there. The right approach depends on what is inside your PDF, and knowing that saves a lot of trial and error.
Know the exact limit
Sizes are written as KB or MB, and 1 MB is 1,000 KB. Some systems count 1,024 bytes to a KB and others count 1,000, so aim a little under the limit rather than exactly at it. A good tool does this for you.
What makes a PDF big
Text is tiny. What makes a PDF large is pictures: scanned pages, photos and screenshots. A text-only PDF of many pages can be smaller than one scanned page.
This tells you how to shrink it. A text PDF can often be shrunk without changing how it looks. A scan can only get smaller by lowering the resolution and quality of its pictures.
Step by step
- Remove pages you do not need. Every page you drop saves space and helps the rest.
- Enter your limit in a compress-to-size tool and run it.
- The tool first tries to shrink the file without touching its pages, which keeps text selectable.
- If that is not enough, each page becomes an image sized to fit, and the space is shared across pages.
- Open the result and check that small print is still readable.
If it still will not fit
- Split the document in two and send it in parts, if the rules allow it.
- Raise the limit slightly if you can. Going from 100 KB to 200 KB makes a large difference to scans.
- Rescan at a lower resolution, in greyscale, or in black and white for pure text.
- Shrink any embedded photos first with an image compressor, then build the PDF from them.
Check before you send
Always open the compressed file and read a page from the middle and the end, not just the first. Check that signatures and stamps are still visible, and that the file size shown by your computer is under the limit.