How to use the compress PDF
- 1Press Choose PDF. The size, page count and whether the PDF has selectable text are shown.
- 2Under Compression mode, choose Keep text or Smallest size.
- 3For Keep text, pick an Image compression level (None, Light, Medium or Strong). For Smallest size, pick a Page image quality and optionally Greyscale.
- 4Press Compress PDF, compare the before and after sizes and the page preview, then press Download.
Measured on a 4-page report with two large photos (4.74 MB)
Keep text · Image compression: Medium
318 KB (93% smaller); 2 images re-saved at lower quality, text still selectable
On a 6-page text-only PDF saved without object streams, Keep text with no image compression went from 21.0 KB to 13.6 KB.
How PDF compression works
A PDF is a container of objects: page descriptions, fonts, images and metadata. Most large PDFs are large because of their images, so that is where real savings come from. This tool offers two honest approaches:
- Keep text rewrites the file: it drops objects nothing refers to, compresses data that was stored uncompressed, packs small objects into compressed object streams and, if you choose an image level, re-saves photos as smaller JPEGs. Text, fonts, links and form fields are untouched.
- Smallest size renders every page to a picture with PDF.js and builds a new PDF from those JPEGs. It reaches much smaller sizes on scans, but the text becomes part of an image.
The result always shows the real before and after size; if a method doesn't make the file smaller, it says so and offers no download.
Choosing a compression level
| Level | What happens to images | Typical use |
|---|---|---|
| None | Nothing; lossless clean-up only | Text documents, forms |
| Light | JPEG 80%, at most 2,400 px long side | Print-quality brochures |
| Medium | JPEG 65%, at most 1,600 px | Email and web |
| Strong | JPEG 50%, at most 1,100 px | Smallest file with text kept |
An image is only replaced when the new version is at least 10% smaller, and small images, masks and unusual colour spaces (CMYK, indexed) are left alone. Measured on the 4.74 MB photo report above: Light gave 1.27 MB, Medium 318 KB and Strong 116 KB.
Scanned PDFs vs text PDFs
A scanned PDF is one big image per page and has no selectable text, which the tool detects and shows after you choose the file. For scans, Smallest size loses nothing you could select and lets you pick the resolution directly. On a 3-page colour scan at 200 DPI (2.55 MB) it produced 782 KB at 150 DPI, 378 KB at 110 DPI and 147 KB at 72 DPI.
For PDFs made from Word or a website, the text is stored as characters and fonts, which are already compact. Turning those pages into pictures makes them bigger: in the same tests a 21 KB text PDF became 1.59 MB at 150 DPI. Use Keep text for them.
When a PDF won't get smaller
Some PDFs are already as small as they can be without losing quality: text-only files saved by modern software, or scans that were compressed well when they were made. Keep text then reports that no smaller file was possible.
Other causes: images in formats the browser can't re-encode (CMYK photos, JPEG 2000), embedded fonts (which this tool doesn't subset) or attached files. Removing pages you don't need with split PDF often saves more than any compression setting.
Compressing to a specific size
If a form or portal states a limit, use compress PDF to 100KB or compress PDF to 50KB. Those pages search for the best quality that fits: first by shrinking images while keeping text, then by rendering pages at the highest resolution that still fits, and they tell you when the target can't be reached at a readable quality. The guide how to reduce PDF file size covers the background.
Are my files uploaded?
This tool runs entirely in your browser. Your PDF files are not uploaded to our servers.