The quickest way: in your browser
- Open the compressor on a computer or phone.
- Choose your PDF, or drop it onto the page. It is read on your device and not uploaded.
- Pick a setting. Recommended suits most files. If a form has a size limit, choose Target size and enter that limit.
- Select Compress PDF, check the result and download it.
The result shows the exact size in bytes. If the file can’t reach your target, the tool says so instead of claiming success, and explains why.
Which setting to choose
- Recommended reduces images to 150 dpi at the size they appear on the page. Text stays sharp and pages still print well.
- Strong goes down to 100 dpi. Use it for email and messaging, where files are viewed on screen.
- Lossless changes no image or letter and only stores the file more efficiently. Savings are usually small, sometimes none.
- Target size looks for the best-quality setting whose result fits, measuring each attempt rather than guessing. Use it when a portal states a limit such as 100 KB or 200 KB.
Why some PDFs barely shrink
How much a PDF can shrink depends on what is inside it:
- Photos and scans usually shrink a lot, because they are often stored at a higher resolution than the page needs.
- Text, fonts and drawings are already compact. They are kept exactly as they are so text stays sharp and selectable, which means they set a floor on how small the file can get.
- Files that were already compressed may have little left to remove.
- Page count matters for scans. Every scanned page is a picture, so a ten-page scan needs far more space than a one-page scan at the same quality.
So the same target can be easy for one file and impossible for another. A one-page scanned certificate can often get under 100 KB; a 20-page colour scan usually can’t without becoming hard to read.
Make the file smaller at the source
If you can create the PDF again, these steps often help more than compressing afterwards:
- Scanning: scan documents in grayscale (or black and white for plain text) at 150 to 200 dpi rather than colour at 300 dpi or more, and crop away empty margins.
- Phone scans: use your scanner app’s document mode, which crops the page and flattens the background, rather than taking an ordinary photo of the paper.
- Microsoft Word on Windows: choose File > Save As, pick PDF as the file type, and under Optimize for select Minimum size (publishing online). Word for Mac offers a similar choice for a smaller PDF meant for electronic distribution.
- Preview on a Mac: open the PDF, choose File > Export, and select Reduce File Size in the Quartz Filter menu. This filter can reduce images heavily, so check photos and small print afterwards and keep the original.
On a phone
The compressor works in current mobile browsers. Choose the PDF from your files, compress it, and download the result; on most phones it is saved to your Downloads folder or the Files app, ready to attach to a form or message.
Phones have less memory than computers, so very large PDFs, roughly 100 MB or more, are better handled on a computer. The tool tells you if a file is too large for your device.
If the file still won’t fit the limit
- Send fewer pages. Remove pages the form doesn’t ask for, or split a long document if the portal accepts several files.
- Rescan with the settings above.
- Check how the limit is counted. Some portals treat 100 KB as 100,000 bytes and others as 102,400 bytes. Aiming for the smaller number passes both; our target sizes do this.
- Check the result before uploading. Open the compressed PDF and make sure small print and signatures are still readable.
How to check a PDF’s file size
- Windows: right-click the file and choose Properties.
- Mac: select the file and press Command + I.
- Android and iPhone: open the file’s details in your Files app.
The size shown there is the size a portal will see.
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