How to compress a PDF so it weighs less
The form says "5 MB maximum" and your PDF weighs 18. Before giving up and sending it in pieces, it helps to know why it is so heavy: the fix depends on that.
4 minute read
Why a PDF gets so heavy
There is almost always a single culprit: images. A twenty-page typed document takes a few hundred kilobytes. That same document scanned with a phone can go past 30 MB, because every page stops being text and becomes a high-resolution photograph.
That is the difference that matters. A text PDF already ships compressed and there is very little left to squeeze. A scanned PDF has plenty of room, because hardly anyone needs their paperwork at 600 dots per inch.
How to tell which one you have
Open it and try to select a word with the mouse, as if you were about to copy it. If you can, it is a text PDF. If the cursor selects the whole page as though it were a photo, it is a scan.
How to compress it
Open the compress PDF tool and drag your file in. You can drop several at once.
Leave it on Automatic unless you have a reason not to. It looks at how the document is built and applies whatever saves most without spoiling it.
Press Compress and wait. On a long scan it takes a few seconds per page.
Check the before and after shown on screen, then download.
The three options, and when each one fits
- Automatic. The right call in practically every case. It tries several routes, measures them and keeps the best.
- Keep the text. When you still need to search inside the document with Ctrl+F, or when someone will have to copy paragraphs out of it. It saves less, but nothing is lost.
- Maximum reduction. For when all that matters is that it fits. Every page becomes an image: it reads and prints fine, but the text stops being selectable.
If nothing comes off
It happens, and it is useful information: it means your PDF was already well optimised. In that case we hand you back the original untouched rather than an equally heavy copy under a new name.
If you still need to get under a hard limit, two roads remain: turn it black and white, which strips a lot from colour scans, or split the document in two and send it in two emails.
What NOT to do
- Put it in a ZIP. A PDF is already compressed inside; a ZIP shaves 2% at best and adds a step for whoever receives it.
- Print to PDF from the viewer. Sometimes it works, but it is a lottery: depending on the program, the result weighs the same or more.
- Drop the resolution by eye. Below 96 dots per inch scanned text starts getting hard to read, and there is no way back.