How to make a PDF smaller for online upload forms
By the Toolbenchly team ·
Upload portals for jobs, admissions, scholarships, visas and government services often limit documents to 100 KB, 200 KB, 500 KB or 1 MB. A certificate scanned with a phone can easily be 3–10 MB. Here's why, and the order of steps that gets almost any document under the limit while keeping it readable.
Why scanned PDFs are so large
A PDF made from a scan or photo stores each page as a picture. Phone cameras capture around 3000×4000 pixels per page, in full colour, at high quality. That's far more detail than anyone needs to read an A4 page on screen. Typed PDFs exported from Word are different: they store text as text and are usually already small.
Step 1: keep only the pages you need
Every page costs space, and page count is the biggest factor you control. If the portal wants just the first page of a mark sheet, or one page per document, remove the rest with Split PDF before anything else.
Step 2: choose the right resolution
Resolution is measured in DPI (dots per inch). For on-screen reading, 100–150 DPI is plenty; at 72 DPI normal text is still readable but small print gets soft. Going from 300 to 100 DPI reduces the pixel count by 9×, which is where most of the saving comes from.
Step 3: use black and white for text documents
Certificates, letters and forms rarely need colour. Converting to grayscale typically saves another 30–50%, and on a clean scan the text even looks crisper. Keep colour only where it carries meaning, such as a coloured photo ID.
Step 4: compress to the exact limit
The PDF Compressor combines these steps: it re-renders each page at a lower resolution, optionally in black and white, and saves it as an optimized JPEG inside a new PDF with the same page size. In Target file size mode you type the limit, for example 200, and it tries settings from sharpest to smallest until the file fits. Shortcuts: 100 KB, 200 KB, 500 KB, 1 MB.
Have photos instead of a PDF?
If you photographed the document, either compress each photo first with the Image Compressor and then combine them with JPG to PDF, or create the PDF first and compress it. Both work. Compressing the PDF is simpler when you have a strict total limit.
How many pages fit?
| Limit | Black and white text pages | Colour pages |
|---|---|---|
| 100 KB | about 1–4 | about 1 |
| 200 KB | about 3–6 | about 1–3 |
| 500 KB | about 8–15 | about 3–6 |
| 1 MB | about 15–30 | about 6–12 |
These are rough figures for clean phone scans; dense pages, shadows and photos need more.
Things to know
- Compressing by re-rendering makes text non-selectable, like a scan. Keep your original file.
- Password-protected PDFs must be unlocked first.
- Always open the compressed file and zoom in before uploading, to check that small print is readable.
- Don't upload ID documents to random websites to compress them. The tools here run entirely on your device.