Make a PDF smaller.

Re-encodes the photographs and scans inside your document — the only part of a PDF that is ever really worth compressing — and then, whenever it has actually re-encoded one, puts the same page up twice, before and after, so you can see what it cost before you throw the original away. When nothing was re-encoded there is nothing to compare: you get the per-image table saying which ones were left alone and why. If your file can’t be usefully compressed, it says so instead of pretending.

$99 once and the whole toolkit is yours — Acrobat is about $155 a year and stops working the day you stop paying. And your file stays on your laptop: we never see it, because nothing you open here is stored on a server.

Questions people actually ask

Where does the file go?: Nowhere. The decoding, the re-encoding and the PDF writing all happen inside this page, so we never see it. The app is served with a Content-Security-Policy that only permits connections back to its own origin, which means the browser itself refuses to let this page open a connection anywhere else — not logs it, refuses it.
What actually gets made smaller?: The pictures. In almost any large PDF, the photographs and scanned pages are the bytes; the text, fonts and vector graphics are a rounding error next to them. So those images are decoded, scaled down if they are larger than they need to be, and re-encoded as JPEG. Everything else in the document is left exactly as it was.
Is it lossy?: Yes, for the images, and it cannot be undone. That is why your original file is never modified — you get a second file, and, whenever an image actually was re-encoded, the same page rendered both ways so you can decide whether the trade is worth it before you replace anything. If nothing was re-encoded there is nothing to compare, and the per-image table says why each one was left alone.
Why did my file barely shrink?: Most likely because it is text and vectors, or because its images are already well compressed, or because they are of a kind we refuse to touch — transparency, indexed colour, CMYK, JPEG 2000, fax encoding. We list every image and say which of those applied. A file that is genuinely already small will be reported as such rather than dressed up as a saving.
Will it break my form fields or bookmarks?: No. The document is modified in place rather than rebuilt, so pages, form fields, links, bookmarks and text all survive. Rewriting it also drops any objects the file was carrying around but no longer using.

Your original file is never modified. Compression is lossy and cannot be reversed, so keep the original until you are sure you are happy with the copy — and remember that the copy is the one you should share.