About Compress PDF
A PDF is usually big for one reason: pictures. A scan is a stack of photographs of pages; a brochure is a handful of high-resolution images with a little text on top. The words themselves take almost no room. So the way to make a PDF smaller is to make its pictures smaller, and the skill is in doing that without making the document look worse than it needs to.
This tool re-encodes the pictures inside your PDF and leaves everything else exactly as it was. Text stays text, vector drawings stay vector, and fonts stay embedded. It runs in your browser, so the file is compressed on your own computer and is never uploaded. You choose how hard it works, and it tells you the size before and after.
How to compress a PDF
- Choose the PDF you want to shrink.
- Pick a level under "How hard". Light changes the pictures least and saves least. Smaller, which is selected to begin with, is the sensible middle. Smallest compresses the pictures hardest and is for when the size limit is the only thing that matters.
- Press the button and wait. A long document with many pictures takes longer, and a progress indicator shows how far it has got.
- Read the result line. It reports the size before and after, the percentage saved and how many pictures were re-encoded, for example "4.2 MB → 1.1 MB, 74% smaller".
- Look at the preview, especially at any page with a photograph or a signature, and save it if it looks acceptable. If it is too soft, run the original again at a lighter level.
When you would use it
- Getting a scanned document under an email attachment limit, or under the size cap on a government or application portal.
- Shrinking a brochure or presentation exported with print-resolution images so it can be shared or downloaded quickly.
- Making an archive of many documents take up less room.
- Preparing a file for a slow connection, where a 40 MB PDF is a real obstacle.
- Reducing a bundle after you have joined it with Merge PDF.
What it will not do
- It only reduces pictures. A PDF that is mostly text may already be as small as it can sensibly be, and the tool says so and returns your original rather than a file that is no smaller.
- Compression of pictures is lossy. The smallest setting can make photographs and fine scanned print visibly softer, and that cannot be undone, so keep the original.
- It does not remove fonts, bookmarks, form fields or metadata, and it does not alter the text. To strip the hidden author and software details, use Remove metadata.
- It does not run character recognition. A scan stays a scan; make it searchable with OCR PDF.
- A file with a password to open it has to be unlocked first.
How it compares
Printing to PDF again or "reducing file size" in a desktop viewer works, but it usually re-renders every page, which can flatten forms, change fonts and turn selectable text into a picture. Re-encoding only the pictures keeps the document structurally the same.
A lot of online compressors upload the file, which is a serious matter for a contract or a medical record, and many reserve their best level for paid accounts. Here the compression happens on your machine, and all three levels are available to everyone.
Tips
- Try Smaller first. If the result is still over your limit, go to Smallest from the original, not from the compressed copy, because compressing twice loses quality twice.
- If a scan is the problem, scanning at a lower resolution to begin with often beats compressing afterwards. 150 to 200 dots per inch is plenty for reading on screen.
- A signature or stamp image can look rougher after compression. Check those first.