Compress a PDF to 500 KB
The target is already set to 500 KB. Your browser re-encodes the pictures inside the document, dropping quality a step at a time until the file fits, and tells you if it cannot get there.
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Nothing here is uploaded. See how the page enforces it.
Who needs 500 KB
Email attachments and ticketing systems. Mail servers cap a whole message at 10 to 25 MB, so 500 KB a document lets you attach a realistic number of them without the message bouncing.
Whether 500 KB is reachable at all
Comfortable. A scan reaches it at a quality that is hard to fault, and most documents that are mostly text are already well under it before you start.
This matters more than the number, because a PDF is only compressible where it holds pictures. A scanner writes one large JPEG per sheet and the text around it costs almost nothing by comparison, so a scan has a great deal to give up. A document exported from a word processor is text, fonts and vector drawing, none of which an image compressor can touch. If yours is the second kind, the row will say there were no pictures to shrink, and that is the honest end of it rather than a failure to work around.
How the target is approached
Re-encoding a whole document is far too expensive to binary-search the way the image tools do, so this walks down a short ladder of quality and resolution steps and stops at the first one that fits under 500 KB. Because the ladder descends, the first fit is also the best looking result available at that size.
Every attempt happens on your own machine, and the document is reloaded from your file each time, so a failed attempt never leaves a mark on the next one. Nothing is uploaded at any point, which is worth knowing when the document is a payslip or a medical letter.
Questions
+ Is the result exactly 500 KB?
It is at or under 512,000 bytes. Landing on the number exactly would mean padding the file, which is not something an upload form wants and not something this does.
+ Nothing happened. My PDF was already under 500 KB.
Then it comes back as it is. Re-encoding a document that already meets the target would cost quality and gain nothing. The row says what it did, including when what it did is nothing.
+ Does it change the text or the page count?
No. Only image streams are rewritten. Text stays selectable and searchable, the page count is unchanged, and no page is flattened into a picture.
+ Are my files uploaded anywhere?
No. The PDF is read and rewritten by your own browser. Open devtools, watch the Network tab while you run it, and nothing leaves. The page keeps working with your connection switched off, which is the part worth caring about when the document is a payslip, a contract or a medical letter.
+ Is there a size limit or a sign-up?
Neither. There is no server paying for your bandwidth, so there is nothing to meter. The practical ceiling is your own device's memory, which on a normal laptop means documents of several hundred megabytes.