Is my document uploaded?
No. Everything runs in this tab using your own browser, there is no network request in this tool, and it works offline. Your document is held in memory only while it is being processed.
Why did this tool not work before?
It was published from an unfinished template. Its two files were the same generic scaffold as Merge PDF and Split PDF, and its processing function returned whatever you typed straight back. Its size figures were the length of that text, so the compression ratio was always exactly 1.
Why did my file barely get smaller?
Almost certainly because it is mostly images, and images cannot be recompressed with the library available here. The tool shows you the bytes per page and says outright when images are likely to be the reason. Removing pages you do not need is the biggest saving available.
Can you not just recompress the images?
Not honestly, no. That needs an image pipeline this project does not have, and adding one is out of scope. A slider that pretended to do it would be exactly the kind of control this rebuild exists to remove.
What if the result is bigger than the original?
Then the tool says so plainly and gives you your original back instead, unchanged. That is the default. A compressor that quietly hands you a bigger file is worse than useless.
What actually makes the file smaller here?
Rebuilding it page by page, which drops orphaned objects and old saved revisions; object-stream compression; removing metadata, JavaScript and attachments; flattening or removing forms; dropping annotations; and above all removing pages.
Will it change how my document looks?
Not with the light or balanced levels. Strong flattens forms, so fields still look right but no longer accept input. Archive also drops links and bookmarks. Each switch says what it costs.
Can I compress a password-protected PDF?
No. It is detected and named. Remove the password in your PDF reader first, then add it again.
Can I set a target size?
Yes, and the tool tells you honestly whether it reached it. When it cannot, it names which options would go further rather than failing quietly.
What are the limits?
One hundred megabytes per file, three hundred in total, and fifty files in one run. If you go over, the message states the real numbers.
Also known as: compress pdf, reduce pdf size, shrink pdf, make pdf smaller, optimise pdf, optimize pdf, pdf compressor, reduce pdf file size, compress pdf offline, compress pdf without uploading.