Why a PDF is too big, and what compression actually does
A PDF is usually oversized for one reason: it contains photographs. A scan, a phone picture of a document, a report full of screenshots — each page is an image, and images do not shrink by being asked politely.
This tool rebuilds each page as an optimised image at the quality level you pick. That is an honest description of a real trade-off: the file gets smaller because the pixels get fewer. There is no lossless magic that halves a scan.
Choosing a level
Start at the lightest setting and look at the result. For a scanned contract that only needs to be readable and emailed, heavier compression is usually fine and the saving is dramatic. For anything with fine print, small figures or a plan drawing, stay light — you can always compress again, but you cannot get detail back.
One thing worth knowing: because pages are re-rendered as images, selectable text in the original becomes part of the picture. If you need the text to stay searchable, compress a copy and keep the original.
When you actually need it
Email attachment limits, still stubbornly around 20–25 MB at most workplaces. Government and bank upload forms that cap at 5 MB or even 2 MB. Job portals that reject anything over a few megabytes. Sending a scanned lease over a mobile connection.
It is also the quiet fix for a document that takes ten seconds to open on someone else's laptop.
What to check before you send the compressed file
Open it. That sounds obvious and it is the step people skip. Compression that looked acceptable in a thumbnail can turn a column of figures into grey mush, and you will not find out until the person on the other end asks you to resend it.
Pay particular attention to the smallest text on the busiest page — a footnote, a reference number, a handwritten annotation. Those degrade first. Signatures and stamps are also worth a look, since they are exactly the part a recipient may need to verify.
If the file still will not fit after heavy compression, the answer is usually not more compression. Split it, send the pages that matter, or put it somewhere and send a link. A document compressed until it is unreadable has not been sent successfully.
What happens to your files
Every one of these runs in your browser. The file is read from your disk, processed in memory and handed back as a download — there is no upload, no server copy and no account.
Compression is the tool people are most tempted to hand to a random website, because the free ones are everywhere. That is exactly the wrong instinct for a scanned passport or a payslip.
Frequently asked questions
Why did my file barely shrink? Because it was mostly text to begin with. Text is already tiny; the savings come from images, so a text-only PDF has little to give up. You can check this quickly: if the original opens instantly and the text is crisp and selectable, there is very little image data to squeeze.
Will the text still be selectable afterwards? No. Pages are rebuilt as images, so text becomes part of the picture. Keep the original if you need searchable text. If searchable text matters to you, compress a copy and archive the original, because the conversion is one-way.
Which level should I pick? Start light and check the result. Heavier settings suit scans that only need to be readable; keep it light for fine print or drawings. It also depends on where the file is going — a portal with a hard 2 MB cap leaves you less room to be gentle than an email attachment.
Is my document uploaded to compress it? No. The rebuild happens in your browser and the smaller file is generated locally. That also means very large documents are limited by your device's memory rather than by an upload size limit.
Related: PDF to JPG · Merge PDF · Split PDF · All tools