To compress a PDF online, open Compress PDF, add the file, choose Best Compression, Average, or Low, and press COMPRESS. The success card then shows the size you uploaded and the size you're about to download. The level you choose decides mainly one thing — how the images inside the document are stored — because text, fonts, and layout come through untouched at every setting. That's why a scanned contract can lose most of its weight while a plain text report barely moves.
This covers:
- The three steps, start to finish
- What Best, Average, and Low actually do, and which one to pick
- How to read the result card, including the "already well compressed" case
- Why some PDFs barely shrink
- Compressing a batch of PDFs in one go
- What to try when the file is still too big, and what to do when something goes wrong
Compress a PDF in three steps
- Open Compress PDF. Nothing to install and no account needed to start.
- Add your PDF. Drop it onto the drop zone, or pick it from your device, Google Drive, or Dropbox. The file shows an upload percentage, then a brief security check before it's ready.
- Choose a level and press COMPRESS. The compression selector in the button bar starts on Best Compression; leave it there unless the next section gives you a reason not to. When the job finishes, the success card shows how much smaller the file got. Download it, or save it straight to Google Drive or Dropbox.
The result is a separate file — the original name with (compressed) added — and the original stays in your list untouched. Trying another level is a matter of changing the selector and pressing the button again.
Got a file that's too big to send?
Try Compress PDFWhat the three compression levels actually do
A PDF's weight is almost always its images: scanned pages, photos, screenshots, logos. Every level keeps the text selectable and the page dimensions unchanged; what differs is how those images are stored afterwards.
| Level | What happens to the images | Pick it when |
|---|---|---|
| Best Compression | Brought down to screen-reading resolution and re-encoded. The smallest file. | Emailing, uploading to a portal, sharing anything that will be read on a screen. The default, and right most of the time. |
| Average | Kept at print resolution and re-encoded more conservatively. | The document will be printed at normal office quality and the images need to survive it. |
| Low | Kept at print resolution with the gentlest re-encoding. The closest to the original, and the largest of the three. | Photography, artwork, anything going to a professional printer, or when you've been told the file must not visibly change. |
Two things follow from that table:
- If a PDF is only text, the level barely matters. There's little for any setting to squeeze, so the file lands close to where it started whichever you choose.
- Best Compression is not a quality gamble for everyday documents. Screen resolution is what you're reading right now, and it prints fine for a contract or a report. Step down to Average or Low for the cases in the table, not by default.
Compress last
Make compressing the final step. If you still need to merge, split, or convert, do that first and compress the finished document once — otherwise the downsampled images ride through every later step, and the last tool can't restore what the first one threw away.
How to read the result
When the job finishes, the success card says We compressed 1 file for followed by the percentage, with the sizes underneath: the size you uploaded, an arrow, and the size of the file you're about to download. The percentage is worked out from those two sizes, so the number you see is the number you get.
Sometimes the card says something else instead: We tried compressing your files, but it looks like it is already well compressed. That means nothing worth having could be squeezed out at the level you chose. You can still download the result, and it is never larger than the file you uploaded — the tool doesn't hand back a PDF that grew.
Why some PDFs barely shrink
The "already well compressed" card usually has one of four causes:
- It's all text. A text-only PDF is already compact. There are no images to downsample, and the level makes almost no difference.
- It has been compressed before. A file exported with a "smallest size" option, or already run through a compressor, has its images at screen resolution already. A second pass at the same level finds nothing new.
- The weight is vector artwork or fonts. Drawings, maps, and charts are lines and curves rather than pictures, and a document that embeds many fonts carries them on every export. The image settings can't touch either.
- It's simply long. Hundreds of pages of modest weight add up, and the fix is fewer pages rather than harder compression.
When the file has to meet a hard limit and Best Compression didn't get there, the section on trimming the document below covers the remaining levers.
Compress several PDFs at once
Add the whole batch and the checkboxes decide what goes in, the same way they do for every tool:
| What you select | What gets compressed |
|---|---|
| Nothing ticked | Every file in the list |
| Some files ticked | Only those files |
The COMPRESS button shows the count in brackets — COMPRESS [ 3 ] — so you can confirm before you commit. Every file is compressed separately at the level you chose, and the card reports the before-and-after totals for the batch. More than one result arrives as a single zip, and the card says how many files are inside.
If you'd rather keep working on the compressed copies here — merge them, split one, or run them again — Add Result to File List puts them into the list next to the originals.
Without an account there's a cap on how many files the workspace holds at once. Compress in batches, or see pricing for the higher limits.
Still too big? Trim the document
There is no setting that targets an exact size. Best Compression shrinks the file as far as its content allows, and whether a target like 1 MB is reachable depends on what's inside. When it isn't enough:
- Step up, don't repeat. If you ran Low or Average, run the original again at Best Compression. Running Best Compression twice gains almost nothing — the images are already at screen resolution after the first pass.
- Send fewer pages. Split PDF pulls out the range you need and Delete PDF Pages drops the ones you don't. Then compress what's left.
- Send one page as a picture. For a single page — a signed form, a certificate — PDF to JPG makes an image small enough to fit anywhere a PDF wouldn't.
- Share a link instead. If the limit is an email attachment cap, save the compressed file to Google Drive or Dropbox from the success card and send a link.
When compressing goes wrong
| What you're seeing | What happened | Fix |
|---|---|---|
| "…seems to be broken, invalid or encrypted" when adding the file | The PDF is password-protected, or damaged, and can't be opened | Remove the password with Unlock PDF first — you'll need the password — then compress. No password? Try Repair PDF |
| "Already well compressed" | Nothing left to squeeze at that level | See the causes above, then trim pages instead of compressing harder |
| A file in the batch was skipped | It couldn't be read | Run it through Repair PDF and try again |
| Printed pages look soft | Best Compression brought the images down to screen resolution | Compress the original again at Average or Low |
| Smaller, but the text won't search | It never had text — it's a scan | Compression keeps what was there; it can't add a text layer |
| Can't add any more files | Without an account there's a cap on how many files the workspace holds at once | Compress in batches, or see pricing for higher limits |
Where compressing fits with the other tools
Compressing is usually the last step of a longer job. The common pairings:
| You want to | Tool |
|---|---|
| Combine files, then shrink the result | Merge PDF first, then Compress PDF — how to merge |
| Send only some pages | Split PDF or Extract PDF Pages — how to split |
| Drop pages before sending | Delete PDF Pages |
| Turn a page into an image | PDF to JPG |
| Remove a password so the file can be compressed | Unlock PDF |
| Fix a file that won't open | Repair PDF |
| Make photos into a PDF in the first place | JPG to PDF |
For the everyday situations where a smaller file pays off — attachment limits, upload caps, full cloud storage — see how compressing PDFs makes everyday tasks easier.
See all PDF tools.
Frequently Asked Questions
Which compression level should I choose?
Best Compression, unless the document will be printed at high quality or contains photographs that must not change. It's the default, it produces the smallest file, and on a screen the difference from the original is hard to spot. Use Average for office printing and Low when the images need to stay as close to the original as possible.
Does compressing a PDF reduce its quality?
The text, fonts, and page layout come through unchanged at every level; only the images are stored more compactly. At Best Compression they're brought down to screen resolution, which reads fine on a display and prints acceptably for ordinary documents. Choose Low if the images need to stay closest to the original.
Why did my PDF barely shrink?
Because there was little to squeeze: it's mostly text, it was already compressed, or its weight is vector artwork rather than images. The success card says so — already well compressed — and the copy you get back is never larger than the one you uploaded. Sending fewer pages is the fix in that case.
Can I compress a PDF to a specific size, like 1 MB or 500 KB?
There's no exact-size setting. Best Compression shrinks the file as far as its content allows; if that's still over the limit, split out the pages you actually need with Split PDF and compress those.
Can I compress several PDFs at once?
Yes. Add the batch, tick the files you want (or none, for all of them), and press COMPRESS. Each file is compressed separately at the level you chose, and the results come back together as one zip. Without an account there's a cap on how many files the workspace holds at once; pricing covers the higher limits.
Does compressing change the page size or make the text unselectable?
No. Pages keep their dimensions, and the text stays selectable and searchable if it was to begin with. A scanned PDF is a picture of a page, and compressing keeps it a picture.
Is it safe to compress a confidential PDF online?
Files travel over an encrypted connection, are processed automatically, and are permanently deleted from our servers within a few hours. If the document can't leave your machine at all, the desktop app compresses offline.
