How to make a PDF smaller for email and upload limits
Why some PDFs are huge, which compression method to choose, and how to reach a target size such as 2 MB or 5 MB without ruining readability.
· 2 min read
Most size limits you'll meet are between 2 and 25 MB: many online application forms cap uploads at 2–5 MB, and email providers typically reject attachments over 20–25 MB. Here's how to get under them.
First, understand where the size comes from
A page of text in a PDF takes only a few kilobytes. What makes PDFs big is almost always images: scanned pages, photos, or screenshots stored at high resolution. A single A4 page scanned in colour at 600 DPI can weigh several megabytes.
So the question is: is your PDF mostly text, or mostly images?
Option 1 — Strong compression (scans and photo-heavy PDFs)
Compress PDF in strong mode renders each page as an image at a lower resolution (80–150 DPI) and stores it as JPEG. For scanned documents this is exactly what you want: they were images already, and 110–150 DPI is perfectly readable on screen and fine for most printing.
Typical results: a 12-page colour scan of 24 MB drops to about 2 MB at the recommended level.
The trade-off: text becomes part of the image, so it can't be selected or searched. Don't use this mode on a contract you'll need to copy text from.
Option 2 — Lossless optimisation (text documents)
Lossless mode rewrites the PDF's internal structure without touching the content. Gains are modest (0–15%). If the tool tells you the file is already optimised, that's accurate: a text-based PDF is already about as small as it gets.
Other ways to hit a size limit
- Split it. If a form accepts several files, use Split PDF to send the document in parts.
- Fix the source. If you're creating the PDF from photos, compress the photos first with Compress Image (1600–2000 px wide is plenty), then combine them with JPG to PDF.
- Scan smarter. Scanning documents in greyscale at 200 DPI instead of colour at 600 DPI makes files 10–20 times smaller from the start.
Is it safe to compress confidential documents online?
With this tool, the PDF never leaves your device: compression runs in your browser. For any service that uploads your file, check where it's processed and how long it's kept before sending sensitive documents.