Compress PDF
Shrink a PDF by re-rendering pages as JPEG at the DPI and quality you choose, or optimise it losslessly. Shows before and after sizes. Files stay on your device.
The interactive tool loads here when JavaScript runs.
About this toolWhat is Compress PDF?
Compress PDF makes a PDF smaller in one of two ways. The strong method renders every page to a JPEG image at the resolution (DPI) and quality you choose and builds a new PDF from those images. The lossless method keeps every word, link and image exactly as it is and only rewrites the file more efficiently.
The strong method gives large savings on scanned documents and photo-heavy files, often turning a 20 MB phone scan into a file small enough to email. Its cost is clear: each page becomes a picture, so text can no longer be selected, searched or copied, links and form fields disappear, and vector drawings become pixels. The tool says so before you run it.
Every result shows the size before and after and the percentage saved. If a method makes the file bigger, which happens with small text-only PDFs, the tool tells you to keep the original. Everything runs in your browser, so the document is never uploaded.
- Strong mode: pages re-rendered as JPEG at 50 to 300 DPI, quality 20 to 95
- Three presets for screen, balanced and print use
- Lossless mode: Flate-compresses raw streams and packs object streams
- Before and after sizes with percentage saved, and a warning when the file grows
- Progress bar with a stop button for long documents
- Runs entirely in your browser: the PDF is read, edited and saved on your device and is never uploaded to a server.
How to use Compress PDF
- Drop a PDF onto the page, or try the sample.
- Pick a method: Strong (pages to JPEG) for scans and photos, or Lossless to keep everything selectable.
- For the strong method choose a preset (96 DPI quality 50, 150 DPI quality 70 or 200 DPI quality 80) or set the DPI and JPEG quality sliders yourself.
- Click Compress PDF and watch the progress; you can stop a long run.
- Compare the before and after sizes. Run the other method or other settings to compare, then download the result you prefer.
Worked examples
Phone scan for email
Input
12-page colour scan, 300 DPI originals, Balanced preset (150 DPI, quality 70)
Output
Typically a large reduction; each Letter page becomes 1275 x 1650 px
Scans gain the most because their pages are already images; halving the DPI alone removes three quarters of the pixels.
Text report from a word processor
Input
2 MB report with embedded fonts, Lossless
Output
Often a few percent smaller, sometimes unchanged
The text is already compressed. The strong method would make it larger and remove selectable text, so keep the original or the lossless copy.
Upload portal with a 5 MB limit
Input
9 MB slide deck exported to PDF with photos, 110 DPI, quality 60
Output
A file to check against the limit before uploading
If the result is still too big, lower the DPI in steps of about 20 before lowering quality, then check that the smallest text is still readable.
Background and insight
Most of the bytes in a large PDF are images. A page scanned at 300 DPI on Letter paper is 2550 x 3300 pixels, about 25 MB as raw 24-bit colour; the scanner usually stores it as JPEG, but often at high quality. Re-rendering the page at 150 DPI keeps a quarter of the pixels (1275 x 1650), and JPEG quality 70 typically cuts each image again by several times. Text-only PDFs are already small because a page of text is a few kilobytes of drawing instructions plus an embedded font, so turning them into images makes them larger, not smaller.
The lossless method does what a PDF library can do without touching content. It finds streams stored with no compression at all (some generators write page content and even images raw) and compresses them with Flate, the zlib/deflate method defined in ISO 32000 section 7.4.4 and RFC 1950/1951. It then packs the many small objects into compressed object streams with a cross-reference stream, a PDF 1.5 feature (sections 7.5.7 and 7.5.8), and drops objects left over from earlier incremental saves. Files from modern office software are usually already compressed, so savings are often small or zero.
DPI and quality are the two dials. 96 to 110 DPI suits reading on screen, 150 DPI keeps small print readable when zoomed, and 200 to 300 DPI is for printing. JPEG quality below about 50 shows ringing and blocky edges around letters. Pages are rendered by pdf.js, the same engine Firefox uses to display PDFs, on a white background.
Common use cases
Email attachments
Get a scanned contract or set of receipts under the 20 to 25 MB limit common mail services set.
Government and job portals
Meet upload caps of 1, 2 or 5 MB on application and tax forms.
Archiving scans
Keep years of scanned letters at a sensible size on a laptop or cloud drive.
Cleaning up generated PDFs
Use the lossless method on files from reporting tools that write uncompressed content streams.
Tips and limitations
- Strong compression turns pages into images. Keep the original if you may need to copy text, fill forms or click links later.
- To make a compressed scan searchable again, run it through Image to Text (OCR) afterwards.
- Lower the DPI before you lower JPEG quality: fewer pixels usually saves more than heavier compression and looks cleaner.
- Check the smallest text at 100% zoom before sending. Footnotes and table figures fail first.
- Very large pages (posters, engineering drawings) are rendered at a lower DPI if needed to stay inside the browser canvas limit of about 16.7 million pixels; the result notes when this happens.
- Encrypted PDFs cannot be optimised losslessly; save an unprotected copy first.
Frequently asked questions
Will compressing my PDF make the text blurry?
With the lossless method, no: nothing on the page changes. With the strong method the text becomes part of an image, so it is as sharp as the DPI allows. 150 DPI is readable on screen; use 200 or more for printing.
Why did my PDF get bigger after compression?
Small text-based PDFs are already efficient, and a picture of a page is larger than the instructions that draw it. The tool flags this; keep your original in that case.
What DPI should I use to compress a scanned PDF?
150 DPI with JPEG quality around 70 is a good balance for documents read on screen. Use 96 to 110 DPI when size matters most, and 200 DPI or more if it will be printed.
Can I still search or copy text after strong compression?
No. Each page becomes a JPEG image. Use the lossless method to keep text, or run the compressed file through OCR to add searchable text back.
What does lossless PDF compression actually change?
It compresses any streams stored without compression, writes objects into compressed object streams and removes leftovers from earlier edits. Text, images, links and forms are unchanged.
Is my PDF uploaded to compress it?
No. Rendering, JPEG encoding and writing the new PDF all happen in your browser tab. The file is never sent to a server.
How small can a PDF get?
It depends on the content. A scanned page at 96 DPI and quality 50 is often well under 100 KB, while a page of vector text cannot shrink much below its fonts and drawing commands.
Is there an in-depth guide to Compress PDF?
Yes. “How PDF Compression Works: DPI, JPEG Quality and Lossless Tricks” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
People also search for
- reduce pdf file size for email attachment
- compress scanned pdf to under 2 mb
- what dpi should i use to compress a pdf
- compress pdf without losing text quality
- why is my scanned pdf so large
- compress pdf for an upload limit
- lossless pdf compression in the browser
- compressed pdf text no longer selectable
Related Tools You May Like
Free, in-browser tools that pair well with this one.