The application form says "max 5 MB". Your PDF is 23 MB. Gmail won't attach anything over 25 MB, Outlook often gives up at 20 MB, and some portals think 1 MB is plenty. No wonder "how to reduce PDF file size" is one of the most searched PDF questions on Google, along with its cousin "why is my PDF so big?"
This guide covers PDF compression from start to finish: why PDFs get huge, what each compression setting actually changes, the order to try things in when you need to get under 1, 5 or 10 MB, and how to do it on a phone. All without making the document unreadable.
How do I reduce a PDF's file size? (The short answer)
- Open Compress PDF and pick your file.
- Start with the "Recommended" level.
- Check the new size on the result screen. Not enough? Change the level and the tool compresses it again.
- Download.
Compressing a PDF is free, needs no sign-up, and your file is processed in your browser. Try as many settings as you like; nothing is uploaded on any attempt.
Why is my PDF file so large?
A text-and-tables document saved from Word with "Save as PDF" is usually a few tens of kilobytes per page. Even a 40-page report rarely goes over 1 MB. If your file is enormous, the culprit is almost always one of these:
- Images. Scanned pages and phone photos carry the real weight. One 12-megapixel photo can be 3–4 MB; ten pages of them make 30 MB.
- Embedded fonts. Lots of custom fonts, or Chinese, Japanese and Korean characters, can take several megabytes.
- Duplicates from merging. Merge ten PDFs that each carry the same logo and the logo may end up in the file ten times.
- Old versions. Some programs append changes to the end of the file on every save, and the old states stay inside.
A quick test: if you can select the text with your mouse and the file is still big, there are high-resolution images inside. If you can't select any text, the pages are pictures already, which means the file is a scan.
A note from Yeti: most of an iceberg is underwater. Most of a PDF's weight is usually hidden too: that "small" logo might really be 3000 pixels wide.
What do the compression levels actually change?
Compress PDF has three levels. In all of them, text and vector drawings stay exactly as they are, so text never gets blurry. Only the images change.
| Level | What it does | When to use it |
|---|---|---|
| Low compression | Shrinks images a little; quality stays almost the same | Documents for print, photo-heavy catalogs |
| Recommended | Brings images down to a resolution that stays sharp on screen | The first thing to try for email and uploads |
| Extreme compression | The smallest file; image loss is noticeable | When nothing else gets you under the limit |
There are two extra options. Convert images to grayscale saves a lot on documents scanned in color that are really black and white (invoices, letters, contracts). Remove metadata deletes title, author and XMP information; it barely affects size, but it keeps stray details out of a document you're about to share.
How do I get a PDF under 1 MB?
If you have a size limit, go in this order and check the size after each step. Most files are done by step two.
- Remove pages you don't need. Blank backs, pages scanned twice, attachments nobody asked for. Remove Pages takes a minute and costs zero quality.
- Compress on the recommended level. Scans usually lose more than half their size.
- Turn on grayscale for black-and-white documents. On a contract scanned in color, this one setting makes a visible difference.
- Try extreme compression, but zoom in and check the result.
- Still too big? Split it. If the portal accepts several files, cut the document up with Split PDF.
Getting under 5 or 10 MB usually ends at step two. For 1 MB and below (or tight limits like 200 KB), you often need steps three and four as well, and for a long scan, step five may be unavoidable.
As a last resort, turning pages into images and back into a PDF also shrinks the file, but the text can no longer be selected or searched. That's usually fine for an application upload; for archiving a contract, avoid it.
How do I compress a PDF on my phone?
On Android and iPhone, Compress PDF runs in the browser; no app needed. PDFs you got through email or a chat app are usually in "Downloads", so pick from there. The compressed file lands in "Downloads" too.
If you're photographing the document yourself, you can solve half the problem up front: the black-and-white filter in Scan Document makes the text clearer and the file smaller.
Make the scan small in the first place
If the file is a scan, half the battle happens while scanning:
- Resolution: 200–300 dpi is enough for text documents. 600 dpi is only for tiny print or pages headed for a printer.
- Color: grayscale or black and white for pages that are just text and signatures.
- Format: JPEG for photo-like pages; PNG makes text scans needlessly large.
Three checks after compressing
Don't hit send the moment you're under the limit:
- Zoom to 150–200% and look at the smallest text: footnotes, table headers, ID numbers.
- Make sure signatures, stamps and seals are still legible.
- Check that the page count hasn't changed.
If something looks broken, go one level down and try again.
Frequently asked questions
Does compressing a PDF reduce quality?
Text and vector graphics aren't touched at all; only images are re-encoded. On "Recommended" you won't see the difference on screen; on "Extreme compression", photos can look soft.
What does "your PDF is already optimized" mean?
There are no images left to shrink. You'll see it with well-made, text-heavy PDFs. If such a file is still big, the cause is probably embedded fonts or attached files: check fonts in Document Properties and strip attachments and hidden data with Sanitize Document.
Can I make a PDF smaller without losing quality?
"Low compression" keeps quality almost identical, and deleting unneeded pages or removing metadata is lossless. For a dramatic reduction, though, the images have to give a little.
Why is a PDF exported from Word so large?
Usually because of the photos in it. Saving with Word's "Compress Pictures" option, or compressing the PDF afterwards, fixes it.
Is it free, and is my file uploaded?
Free, with no sign-up. Your file is compressed in your browser and never uploaded to a server.
In short
The order for reducing PDF file size: delete unneeded pages, compress on recommended, turn on grayscale for black-and-white documents, go extreme if you must, split if nothing else works. Zoom in once before sending; Yeti handles the rest.