Compress PDF Online Free — Reduce PDF Size

PDFs balloon for one reason more than any other: the images inside them. A scanned contract or a photo-heavy report can easily run to 30 or 40 MB, which is past most email attachment limits and past plenty of upload forms too.

This compressor works entirely in your browser — your document is never uploaded, which matters more for PDFs than for almost anything else, because they are so often contracts, invoices, medical letters and ID scans.

How to use Compress PDF

Add your PDF. Drag it onto the box above, or tap to browse.
Choose how hard to try. Rebuild is lossless and keeps your text selectable. Flatten to images shrinks far more but turns the pages into pictures.
If you flattened, pick a detail level. 110 DPI reads well on screen; 150 DPI is comfortable to print.
Click Compress PDF, check the saving, and download.

Why some PDFs will not get smaller

It is worth being blunt about this, because most compressors are not. If a PDF was produced properly — exported from Word, LaTeX or a design tool — it is mostly text and vector drawing instructions, and those are already stored compressed. There is nothing meaningful left to squeeze. A tool that claims a big saving on a file like that is usually just throwing away image quality you did not ask it to touch.

The PDFs that compress dramatically are the ones built from pictures: scans, phone photos of documents, exported slide decks. That is where flattening turns 40 MB into 2 MB.

Rebuild vs flatten

Rebuild reloads the document, drops objects nothing references any more, and repacks the internal structure using object streams. Your text stays real text — selectable, searchable, and readable by a screen reader. Typical saving is 0–25%.

Flatten to images redraws every page as a picture and builds a new PDF from those. Savings on a scanned document are routinely 80–95%. The cost is real and permanent: the text layer is gone, so you cannot search, select or copy from it afterwards, and it is no longer accessible to screen readers. Use it for scans and printouts — not for a contract you still need to search.

How to pick a detail level

72 DPI — fine for reading on a phone or screen, visibly soft in print.
110 DPI — the balanced default. Clear on any screen, acceptable printed.
150 DPI — prints cleanly. The usual choice for a document someone will put on paper.
200 DPI — for fine print and detailed diagrams that must stay sharp.

The grayscale option is worth trying on any black-and-white scan. Removing the colour channels from a document that had no real colour in it often takes another 30–40% off with no visible change at all.

Still too big?

Split it. A 200-page manual will never reach an email attachment limit in one piece — use the PDF splitter to send it in parts, which is also kinder to whoever has to read it.

Frequently asked questions

Why did my PDF barely get smaller?

Because it was already efficient. A PDF exported from Word, Google Docs or LaTeX is mostly text and vector instructions, which are stored compressed already. There is genuinely nothing left to remove. Big savings come from PDFs full of images — scans and photos — which is what the flatten option targets.

What is the difference between rebuild and flatten?

Rebuild is lossless: it repacks the file and drops unreferenced objects, and your text stays selectable and searchable. Flatten redraws each page as an image, which shrinks scans by 80–95% but permanently removes the text layer — you will not be able to search, select or copy from the result.

Is my PDF uploaded to a server?

No. Everything happens in your browser. That matters more for PDFs than for most files, because they are so often contracts, invoices, bank statements and ID scans — none of which should be sitting on a stranger's server.

Will the text still be searchable afterwards?

With rebuild, yes — nothing about the text changes. With flatten, no. The pages become pictures of text rather than text, so search, selection and screen readers all stop working. Choose rebuild whenever that matters.

What DPI should I choose?

110 DPI is the balanced default and reads cleanly on any screen. Use 150 DPI if the document will be printed, 72 DPI if it is only ever going to be read on a phone, and 200 DPI for fine print or detailed diagrams.

Can it compress a password-protected PDF?

Only if it opens without a password. A PDF with an owner password that merely restricts printing will usually load, but one that needs a password to open cannot be read at all until it is unlocked first.

How big a PDF can it handle?

There is no fixed limit, but flattening is memory-hungry because each page is rendered as a bitmap. A few hundred pages at 110 DPI is comfortable on a desktop; a very long document at 200 DPI may exhaust a phone. Pages are processed one at a time and released as it goes, which is what keeps that manageable.