Guide · PDF
Compress PDF files offline on Windows
To make a PDF smaller without uploading it, add it to Crunchy, pick the Balanced level or a target size such as 25 MB, and press Compress. Crunchy does the work on your own PC and writes a smaller copy; the original stays as it was.
01 / What Crunchy does
What happens inside your PDF.
Most of a big PDF is usually pictures: scanned pages, photos, screenshots. Crunchy works on those and on the leftovers around them, and never turns real text into an image.
Scanned pages become 1-bit
On Balanced and Maximum, pages that are black-and-white text or handwriting are stored as sharp 1-bit CCITT G4 images, the format fax-style scans were made for. Only pages with no colour, mostly paper and real dark ink qualify.
Colour stays colour
Photos, shaded artwork, pale backgrounds and colour stamps never qualify for 1-bit. Photos are re-encoded as JPEG (grey ones as greyscale), and flat artwork such as charts is kept exact.
Images sized to the page
Pictures stored far bigger than they're drawn are downsampled to 200 dpi of their size on the page on Balanced, or 144 dpi on Maximum. Light never downsamples.
Duplicates merged
Identical images and streams are stored once. Unused resources, page thumbnails and editor leftovers are dropped.
Fonts slimmed
Embedded fonts lose tables PDF viewers never read. PDFs exported from Word with emoji fonts shrank by 95% or more when this arrived in version 1.0.2.
Checked before it's saved
Everything else is repacked at the highest setting, then the new PDF is reopened and its page count checked. If the result isn't smaller, Crunchy keeps the original bytes and marks it Already optimized.
02 / Pick a level
Which setting to use for a PDF.
- Balanced (the default) for everyday PDFs and scanned documents. This is where scans turn into 1-bit pages.
- Maximum when size matters most: stronger photo compression and 144 dpi images.
- Light for PDFs you'll print or archive: visually lossless, no downsampling, scans left as they are. The Archive preset uses it and keeps metadata.
- Email preset: Balanced, metadata stripped and every file under 20 MB.
Need it under a size limit?
Switch on Target size and type the limit, for example 25 MB for a Gmail attachment. Crunchy compresses the file at your level first; if it's still too big, it tries stronger settings, at most five passes, and keeps the gentlest version that fits.
It won't wreck a file to get there: PDF photos stay at 96 dpi or more and text scans at 200 dpi or more. If the goal is out of reach, you get the smallest version, marked over target, for example "Closest: 27.1 MB (target 25 MB)".
03 / How to
Compress a PDF in three steps.
Add the PDF
Drag it onto the Crunchy window, paste it with Ctrl+V, or right-click it in Explorer and choose Compress with Crunchy. Whole folders work too.
Choose how small
Keep Balanced, pick a preset like Email, or switch on Target size and enter a limit such as 25 MB.
Compress
Press Compress. Check the result with the before/after slider, then send it. Your original PDF is untouched.
crunchy --target 25MB scan.pdfcrunchy --level maximum --out D:\Small *.pdfWorks in PowerShell or Command Prompt once Crunchy is on your PATH (an optional box in the installer).
FAQ
Common questions.
More answers in the main FAQ.
Will compressing a PDF with Crunchy make the text blurry?
No. Real text in a PDF stays text: Crunchy only recompresses the images inside and slims the fonts, so text stays as sharp as before. Scanned pages are pictures, and Crunchy stores black-and-white text scans as crisp 1-bit images at up to 300 dpi; even when it is chasing a target size, text scans never go below 200 dpi.
Will colour stamps or photos in a scanned PDF turn black and white?
No. Crunchy only converts pages that really are black-and-white text or handwriting: no colour, mostly paper and real dark ink. Photos, shaded artwork, pale backgrounds and colour stamps never qualify, so those pages keep their colour.
How long does Crunchy take to compress a large PDF?
Usually seconds, not minutes. Crunchy compresses the images inside a PDF on every CPU core in parallel; for the 1.0.2 release a 268 MB PDF took 16 seconds instead of 66. The time depends on your PC and on how many images the file contains.
Ready to crunch?
Free for Windows 10 & 11. No uploads, no account, no size limits.