Compress PDF
Try to make a PDF smaller and see the honest result: the exact size before and after, and your original back if nothing was saved.
Rewrites the file's internal structure more compactly. Nothing visible changes. Savings are often small, and some files do not shrink at all.
Lower numbers give smaller files and more visible blur.
Your PDF is processed inside your browser. It is not uploaded to our server.
How to use the Compress PDF
- Drop a PDF onto the box, or click it to choose one.
- Start with Re-save. It keeps everything as it is and only stores the file more compactly.
- Press Compress PDF and compare the two sizes. If the file did not get smaller, the page says so and offers your original.
- If the PDF is mostly scans or photos and still too big, switch to Strong, pick a resolution and quality, and try again. Check the result before you send it.
What each method actually does
Re-save opens the PDF with the open-source pdf-lib library and writes it out again using object streams, a feature of newer PDF versions that packs many of the file's small internal objects into one compressed block. If a file was edited and saved several times, it also keeps only the latest version of each object. It does not touch images or fonts, so the gain depends entirely on how the original was written. Many PDFs are already stored compactly, and then the saving is small or zero. You see the real numbers either way.
Strong renders every page with PDF.js, Mozilla's open-source PDF renderer, saves each page as a JPEG at the resolution and quality you choose, and builds a new PDF from those pictures at the original page size. A PDF page is measured in units of 1/72 inch, so 72 dpi gives one image pixel per unit; 150 dpi gives about 1,240 × 1,754 pixels for an A4 page. This can shrink scanned documents and photo-heavy files a lot, but it is a one-way conversion.
What the strong method gives up
- Text becomes part of a picture. You can no longer select, search, copy or have it read aloud by a screen reader.
- Links, bookmarks, form fields, comments and attachments are not carried over.
- Small print and thin lines can look blurry, especially at 72 or 100 dpi.
- Text-only PDFs can get larger, because a page of text is stored very efficiently as text and much less efficiently as a photo of text.
If your PDF is large because of a few big photos, another route is to shrink the photos with Compress Image and recreate the PDF from the source document. That keeps the text real.
Frequently asked questions
Why did my PDF hardly get smaller?
Most of a PDF's size usually comes from images and embedded fonts, and the re-save method leaves both untouched. If the original program already wrote the file compactly, there is little left to gain. The tool tells you when the new file is not smaller so you can keep the original.
Is my PDF uploaded to a server?
No. Both methods run with JavaScript in your browser. The pdf-lib and PDF.js libraries are downloaded to your device; your file is not sent anywhere.
Which resolution should I choose for the strong method?
100 dpi is usually readable on a screen. Choose 150 dpi or more if the document will be printed or has small print. Lower settings give smaller files but blurrier pages.
Can it compress password-protected PDFs?
The re-save method cannot open any encrypted PDF. The strong method can process files that open without a password but carry editing restrictions; the result is an unprotected image-only PDF. Files that need a password to open cannot be processed.
Will the strong method keep my text searchable?
No. Each page becomes a JPEG image, so the text is no longer text. Use it only when a smaller file matters more than selectable text, and keep the original.
Sources: Adobe Acrobat SDK: Coordinate systems (one unit of default user space is 1/72 inch)