How this PDF compressor works
A PDF is a container. Inside it are pages made of text, fonts, vector shapes and images. In almost every oversized PDF, the images are the problem: a phone photo of a receipt, a 600 dpi scan, or a brochure full of high-resolution pictures. Text barely takes any space.
So instead of turning your pages into pictures (which many free tools do, and which makes text blurry and unsearchable), this tool goes through every image inside the PDF and:
- Decodes it, including the awkward formats found in real-world files: CMYK print images, JPEG 2000, 16-bit and palette-based images.
- Downsizes it if it is far larger than needed for screen or office printing.
- Re-encodes it as an efficient JPEG, or as one-bit black-and-white if it is a scanned page of text.
- Keeps the result only if it is smaller. Images that are already compact are left untouched.
After that, unused data left behind by editing programs is removed, duplicate copies of the same image or font are merged, and the PDF is saved with compressed object streams. Nothing about the page layout changes.
Choosing a compression level
| Level | What it does | Good for |
|---|---|---|
| High quality | Light recompression, images up to about 2400 px | Printing, portfolios, photo-heavy brochures |
| Balanced | Images up to about 1800 px; scans converted to clean black-and-white | Email attachments, most upload portals |
| Smallest | Stronger recompression, images up to about 1300 px | Strict size limits, slow connections |
You can switch levels after compressing: the tool re-runs on the same file so you can compare sizes before downloading.
Scanned PDFs get special treatment
A scanned letter is a photograph of paper. The faint texture and grey tone of the paper is “detail” to a JPEG encoder, and it eats most of the file size. When the Balanced or Smallest level sees an image that looks like a scanned page, it lifts the paper to pure white, darkens the ink, and stores the page as one-bit black-and-white at around 200 dpi. A 1.7 MB scan can drop to around 120 KB this way while becoming easier to read. If the scan contains a hidden OCR text layer, that layer is preserved, so the document stays searchable.
Colour photos, charts and screenshots are detected separately and never converted to black-and-white.
What we will never do to your file
- Return a bigger file. If compression doesn’t help, you get your original back and we tell you so.
- Flatten fillable forms. Form fields and their values stay editable.
- Touch transparency masks. Logos and cut-out images keep their transparent edges.
- Upload anything. All processing happens in your browser’s memory, and the result is cleared when you close the tab.
Tips for the smallest files
- If you need to hit an exact limit for a visa, university or job portal, use Compress PDF to 200 KB or 100 KB. They search for the best quality that fits.
- Scanning? Scan in greyscale at 200–300 dpi rather than colour; you’ll start from a smaller file.
- Combining several documents? Merge them first, then compress once.
- Password-protected PDFs must be unlocked before they can be compressed.
Frequently asked questions
Is my PDF uploaded anywhere?
No. The compressor runs inside your browser tab. Your PDF is read and rebuilt on your own device and never sent to a server, which makes it safe for contracts, tax documents and ID scans.
Will the text in my PDF become blurry?
No. We only recompress the pictures inside the PDF. Text, vector drawings and fonts are kept exactly as they are, so they stay sharp at any zoom level and remain searchable and selectable.
Why did my PDF barely get smaller?
Some PDFs are mostly text and embedded fonts, with few or no images. There is little to remove without damaging the document, so the savings are small. If a file can't be made smaller at all, we give you back your original instead of a bigger copy.
Which compression level should I pick?
Balanced suits email and most upload forms. High quality keeps photos close to the original for printing. Smallest squeezes images harder for strict size limits. If you need a specific size, use our compress-to-200 KB or 100 KB tools, which guarantee the limit.
Does it work with scanned documents?
Yes, and scans usually shrink the most. Balanced and Smallest detect scanned paper, clean up the grey background and store the page as crisp black-and-white, which is both smaller and easier to read.