UtilibyWritten by the Utiliby editorial team · Last updated October 13, 2026 · Rules and formulas reviewed October 2026
What this free PDF compressor does
Large PDFs are a daily annoyance: the email bounces because the attachment is too big, a job portal accepts only files under 2 MB, or a scanned contract takes forever to open on a phone. Online compressors solve this, but most upload your document to their servers and limit the free version to a few files per day. This free online Compress PDF tool shrinks your file inside your browser, with no upload, no sign-up and no watermark.
It offers three methods. Smart finds the pictures stored inside the PDF and re-saves them at a lower quality and size, while text, links and vector graphics stay untouched. Strong turns every page into a compressed picture for the smallest files. Lossless only tidies the file structure and can remove metadata. You can pick a level, or enter a target size such as 200 KB or 1 MB and let the tool search for settings that fit. A before and after preview and a size bar chart show exactly what changed.
How to compress a PDF
- Choose your PDF. The page count, size and a preview of page 1 appear.
- Pick a method. Smart for most files. Strong for the smallest size when text selection does not matter. Lossless for no quality loss.
- Pick a level or a target. Recommended is a good balance. Or type a target size in KB and the tool tries stronger settings step by step.
- Click Compress PDF. A progress bar shows each image or page.
- Compare. Check the after preview and the size bars. Zoom in on your own copy if the document has fine print.
- Download. Click Download compressed PDF. Keep your original.
Smart, Strong or Lossless: which method?
| Smart | Strong | Lossless | |
|---|---|---|---|
| What it does | Recompresses pictures inside the PDF | Renders each page as a compressed picture | Tidies structure, strips metadata |
| Text stays selectable | Yes | No | Yes |
| Links and vector graphics | Kept | Lost | Kept |
| Typical saving | Large for photo and scan PDFs | Largest | Small |
| Quality loss | Pictures only | Whole page | None |
| Best for | Reports, brochures, scans with text | Image-only scans, emergency size limits | Already optimized files |
Compressing to a target size
Many forms demand a file under a fixed size, such as 100 KB, 200 KB, 500 KB, 1 MB or 2 MB. Enter that number as the target size in KB (1 MB is 1024 KB) and click Compress. The tool starts with gentle settings and moves to stronger ones, each time checking the size of the result, until the file fits or the strongest setting has been tried. The result and the number of tries are shown. If the target cannot be reached, the best result is kept and a note tells you. A long document with many pictures may not fit a very small target with the Smart method. In that case try Strong, split the document into parts with the Split PDF tool, or remove pages that are not needed.
Why PDFs get big, and what compression can do
The size of a PDF is nearly always determined by its pictures. A single photo from a phone camera can be several megabytes, and a scanned page at 300 dpi in color can be one to three megabytes by itself. Text, by contrast, takes only a few kilobytes per page. Compression therefore concentrates on the pictures. The Smart method decodes each picture, reduces its pixel dimensions if it is larger than needed for viewing, saves it again as a JPEG at a lower quality setting, and puts it back into the same place in the PDF. Pictures that are small, already tiny, used as masks or in unusual color spaces are left untouched. The result is usually dramatically smaller and still looks good on screen.
How much quality will I lose?
- Light: pictures limited to about 2000 pixels at 75 percent quality. Hard to tell from the original on screen.
- Recommended: about 1300 pixels at 55 percent quality. Good for reading and email, small text in photos stays readable.
- Extreme: about 800 pixels at 35 percent quality. Visible softening, but very small files.
- Strong method: pages are drawn at 170 to 60 dpi depending on the level.
Printing at full size needs more detail than a screen. If the PDF is for print, use Light or Lossless and check a printed page.
Tips for getting small PDFs
- If you made the PDF yourself, export it with a lower image resolution from the source program.
- Remove unneeded pages first with the Split PDF tool.
- For scans, scan in grayscale or black and white at 150 to 200 dpi when color is not needed.
- Run Smart first. Use Strong only if the file is still too large.
- Do not compress an already compressed copy again and again, because quality drops each time.
- Keep the original file in case you need full quality later.
Troubleshooting
- No savings. The file may be text-only or already optimized. Try Strong or a target size.
- The result is larger. The tool keeps the smaller of the settings it tries when a target is set. Without a target, choose a stronger level.
- Text looks blurry. Strong at a low level makes text soft. Use Smart or the Light level.
- The browser runs out of memory. Close other tabs, or split a very large PDF and compress the parts.
- Password message. Unlock the PDF first.
What this tool does not do
It does not use server-side optimization, so results can differ from desktop tools that rewrite fonts and images in more ways. It does not run OCR, repair damaged files or keep digital signatures. Images in uncommon formats such as JPEG 2000, JBIG2 or CMYK are left as they are, which can limit the savings on some scanned documents.
Common size limits and how to meet them
| Where the file goes | Typical limit | Suggested setting |
|---|---|---|
| Government or university portals | 100 KB to 2 MB per file | Smart at Extreme, or a target size |
| Job application sites | 2 to 5 MB | Smart at Recommended |
| Email attachments | Around 20 to 25 MB in total | Smart at Recommended, check your provider |
| Messaging apps | Varies, often over 100 MB | Light or Recommended for quality |
| Archiving | None | Lossless, to keep full quality |
Limits change, so check the current rule of the site or service. Enter the limit as a target in KB (1 MB = 1024 KB) and keep a little room below it, because sites sometimes count size differently.
Compressing scans, presentations and forms
Scanned documents shrink the most. A color scan at 300 dpi can be 2 MB per page, but at 1300 pixels wide and 55 percent quality it is often 150 to 250 KB and still readable. Presentations exported to PDF usually hold large photos and shrink well with the Smart method. Forms are mostly text and shrink little, so use Lossless or leave them as they are. Documents with embedded fonts and vector charts are already compact, and the main saving is in any photos inside them. Image-only PDFs made from phone photos benefit from Smart or Strong.
If you need to both merge and compress, merge first and compress the combined file once. Compressing each part separately and then merging gives about the same result, but repeated compression of the same pictures reduces quality, so avoid compressing a file that has already been compressed.
After compression, always look at the result. Zoom into small print, signatures and stamps, and make sure that nothing important became unreadable. If something did, return to the original file and use a lighter level, a larger target size or the Lossless method.
Privacy and how it works
Your PDF is read and rewritten in your browser. Nothing is uploaded, stored or logged. The libraries that read and write PDFs are loaded from a public CDN the first time you use the tool, so you must be online at that moment. Closing the tab clears all files from memory.
Frequently asked questions
How do I compress a PDF for free?
Choose your PDF, keep the Smart method and Recommended level, and click Compress PDF. When it finishes, compare the before and after previews and click Download compressed PDF. There is no account, watermark or size limit beyond what your device can handle.
Is my PDF uploaded to a server?
No. The compression runs in your browser on your own device. The PDF libraries are loaded from a public CDN the first time you use the tool, but your document is never sent anywhere.
What is the difference between Smart and Strong?
Smart finds the pictures inside the PDF and re-saves them at a lower quality or size, keeping text, links and vector art. Strong turns each page into one compressed picture, which gives the smallest files but removes selectable text.
Can I compress a PDF to a specific size like 200 KB or 1 MB?
Yes. Enter a Target size in KB, for example 200 or 1024, and the tool tries stronger and stronger settings until the file is under that size or it reaches its limit. Very small targets for long documents may not be reachable.
How much smaller will my PDF get?
It depends on what is inside. PDFs with large photos or scans can shrink by 70 to 95 percent. Text-only PDFs and files that were already optimized may shrink very little, and the tool will tell you if there is no gain.
Will the quality get worse?
Pictures lose some detail in Smart and Strong modes. Light keeps quality close to the original, Recommended is a good balance for screens and email, and Extreme is for the smallest size. Always compare the preview with the original.
Will the text stay selectable?
In Smart and Lossless modes yes. In Strong mode no, because pages become pictures.
What does Lossless do?
It rewrites the file structure more compactly and can strip metadata. Nothing is changed visually, but savings are usually small.
Why did my PDF not get smaller?
The file may already be compressed, may be mostly text, or may use image formats that the tool leaves alone. Try the Strong method or a lower target size.
Can I compress a scanned PDF?
Yes. Scans are large images, so they usually shrink a lot. Use Smart first. Use Strong or a target size if you need it even smaller.
Can I compress PDF to send by email?
Yes. Most email services limit attachments to around 20 to 25 MB. Check your provider's current limit, then set a target size slightly below it.
Does it remove metadata?
Tick Remove title, author and other metadata to blank those fields. Page content is not affected.
Does compression keep digital signatures and forms?
Any change to a PDF invalidates a digital signature. Form fields are kept in Smart and Lossless modes and are flattened into the pictures in Strong mode.
Is there a file size limit?
There is no fixed limit, but very large PDFs need a lot of memory in the browser. Close other tabs, or split the file first.
Does it work with password-protected PDFs?
Not directly. Remove the password first in the program that created the PDF, or print to a new PDF.
Will it work on a phone?
Yes, in a modern browser. Large files may be slow on older phones.
What can I print or save?
Download compressed PDF saves the result. Print / save summary prints the sizes, a before and after bar chart and page previews, and Copy summary copies the details as text.
Sources and further reading
- Adobe / ISO 32000-1:2008, Section 8.9 Images and Section 7.4 Filters (DCTDecode, FlateDecode, ASCII85Decode), for how images are stored and compressed in PDF.
- pdf-lib documentation, PDFDocument.save with object streams, and the low-level PDFRawStream API.
- ITU-T T.81 / ISO 10918-1, JPEG standard, for the lossy image compression used for PDF pictures.
- Mozilla PDF.js documentation, for rendering pages to images in the browser.
Sources were consulted in October 2026. Standards and rules can change, so always check the official page for your situation.