Compress PDF

Quick Answer: Compress PDF makes a PDF file smaller. It does this by shrinking pictures inside the file and removing extra data you cannot see. You use it when a file is too big to attach to an email or upload to a form.

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What it does, in plain words

To compress means to squeeze. A PDF can be large for two reasons. The first reason is pictures. A photo inside a PDF can be much larger than the text. The second reason is hidden data, like a copy of a font, which is the style of the letters, saved inside the file. Compress PDF reduces that bulk. The pages stay in the same order. The words stay the same. Only the file size goes down.

Compression is a trade. If you squeeze too hard, pictures can look blurry and small text can be hard to read. A good result is a file that is small enough to send, but still clear enough to read and print. Always keep your original file. Then you can try again if the first result looks too blurry.

How to use Compress PDF — step by step

Open the Compress PDF tool on PDFOnlineEditor.
Choose the PDF that is too large. Note its size before you start, so you can compare it later.
Pick a compression level if the tool offers one. If you are not sure, pick the middle or balanced level first.
Click the process or compress button, and wait for the download link.
Open the new file. Read one page of text and look at one picture. If both are clear, the file is ready to send.

A worked example

Ahmed has a 30 MB file. Gmail will not accept it, because Gmail limits attachments to 25 MB. He needs to compress pdf for email under 25mb gmail limit. He opens Compress PDF, uploads the file, and picks the balanced level. The new file is 12 MB. He opens it, reads page 1, and checks a photo on page 4. The text is sharp. The photo is a little softer, but still clear. Now the file attaches to his email with room to spare.

Aim well under the limit, not just under it. Email systems count size in different ways, and a file at 24.9 MB can still be rejected. A file at 12 MB is safe. Outlook limits attachments to 20 MB, and some work systems limit them to about 10 MB, so check the limit of the person you are sending to.

What to check before you send it

The new size. Is it under the email or upload limit, with room to spare?
One page of text. Can you read it easily, without zooming in more than usual?
One picture. Is it still clear enough for its purpose? A photo for a report can be softer than a photo for print.
The page count. The compressed file should have the same number of pages as the original.

3 common mistakes

Compressing the same file again and again. Each round can make pictures worse. Compress once, from the original.
Deleting the original after the first try. If the result is too blurry, you need the original to try a gentler level.
Sending without opening the result. A file can be small and still unreadable. Size alone is not proof of quality.

Honest limits — please read this

Compress PDF is built with pdf-lib, and its output still needs a check on your own file. If a file is already small, or its pictures are already squeezed, it may shrink only a little. That is normal, not a fault. A scanned file, which is a photo of pages, is hard to shrink without making text unreadable, so you may need to split it instead, or send it as a link. A password-protected file will not work until you unlock your own copy first. A very large file can be slow on a phone.

Frequently asked questions

How small will my file become?

It depends on the pictures inside it. A file full of large photos can shrink a lot. A file that is mostly text may shrink only a little.

Will compression change my words or page order?

No. Compression should not change words, page order, or page count. If any of those change, do not use that result. Use the original and try again.

Can I compress a scanned PDF without making it unreadable?

Only a little. Scanned pages are pictures, so squeezing them makes the text softer fast. Try a gentle level first, and check one page of text before you send it.

Related tools

Original Compress PDF tool • PDF Guides • Support: support@pdfonlineeditor.com