Shrink a PDF's file size right in your browser by re-encoding its embedded images at a lower quality — pick low, medium, or high compression and see the before/after size instantly. Nothing is ever uploaded to a server.
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Large PDF files are inconvenient in almost every context they get shared: email providers commonly cap attachments around 20-25 MB, messaging apps impose their own limits, cloud storage quotas fill up faster with oversized files, and a large PDF simply takes longer to upload, download, and open — especially on a mobile connection. Scanned documents and photo-heavy reports are the most common culprits, since a handful of high-resolution scanned pages can easily balloon a file to tens of megabytes even though the actual content, viewed on a typical screen, doesn't need anywhere near that much image data.
Compressing a PDF before sharing it solves this directly: the file becomes easier to email, faster to upload to a portal, and lighter to store in bulk, all while keeping the same page count, layout, and text. This matters constantly in ordinary work — attaching a scanned signed contract to an email, uploading a portfolio of design proofs to a client review tool, or archiving years of scanned paperwork without running out of storage space.
A PDF's file size comes from several sources — text and font data, vector graphics instructions, document structure overhead, and embedded raster images — but in the vast majority of real-world large PDFs, embedded images dominate the total by a wide margin, often accounting for 90% or more of the file. This tool focuses its compression effort exactly there: it scans the PDF's internal object structure for embedded JPEG images, decodes each one using the browser's native image decoder, redraws it onto an in-memory canvas at your chosen quality and (for Medium and High levels) a capped resolution, then re-encodes it as a new, smaller JPEG and swaps it back into the PDF in place of the original.
Because this operates directly on the PDF's internal objects rather than rasterizing entire pages into flat images, every other element on the page — searchable text, vector lines and shapes, fonts, and form fields — passes through completely unchanged. The PDF is then re-saved using object stream compression, which shrinks the document's internal structural overhead a bit further on top of the image savings.
This tool specifically targets JPEG-encoded images (identified internally by the DCTDecode filter), because JPEG is by far the most common format for photographic and scanned content embedded in PDFs, and because JPEG's lossy compression has a well-understood quality dial that maps directly onto meaningful file size reduction. PDFs can also contain images stored with other internal encodings — most commonly a raw, uncompressed-style format typically used for content that started life as a PNG — which this tool leaves untouched, since safely decoding and re-encoding every possible internal PDF image encoding losslessly is a much larger undertaking than a browser-based tool can responsibly cover.
In practice, this means PDFs built primarily from scanned pages or embedded photographs (almost always stored as JPEG internally) see the tool's full compression benefit, while PDFs whose images originated as PNGs or vector exports may see smaller gains, since compression here is intentionally scoped to what can be re-encoded safely and predictably.
Start with Medium for most everyday needs — it applies meaningfully aggressive compression and a sensible resolution cap without pushing image quality low enough to be distracting on a typical screen or printout. Reach for Low when a document's images matter for detailed viewing (product photography, design proofs, anything that might be zoomed into or printed at a larger size) and you'd rather keep a bigger file than risk visible quality loss. Reach for High when you're hitting a hard size limit — an email attachment cap, an upload portal restriction, or simply wanting the smallest possible archive size — and can accept that embedded photos will look noticeably softer in exchange.
Because this tool shows you the exact before/after size for whichever level you choose, the most reliable approach when file size matters is simply trying Medium first, checking whether the result is small enough, and stepping up to High only if it isn't — rather than guessing which level you'll need in advance.
Compress PDF shrinks file size without changing page count. These related PDF tools cover the rest of a typical PDF workflow — combining and splitting documents, and converting to and from images.