Make a PDF smaller by re-rendering the pages — optionally also to grayscale (black and white) for an even smaller file. Strong compression gives the smallest files, but the text is no longer selectable afterwards (like a scan).
Works best on PDFs with lots of images or scans. On already-optimised, text-light PDFs the result can turn out larger — we tell you when that happens and you keep the original.
All tools run entirely in your browser: nothing is sent to the server. A password-protected PDF will not open here; remove the protection first with the Unlock tool.
Most mail servers don't measure your file, they measure the encoded copy that travels. An attachment is turned into text along the way and grows by about a third in the process. A 9 MB PDF therefore crosses a 10 MB limit and bounces, often a quarter of an hour later. So set your target size well below the limit you have to meet: 7 MB where 10 is allowed, 18 MB where 25 is. If the file is still too large after that, send it as a download link instead of an attachment.
A level applies one fixed setting, and you only find out afterwards what it saved. A target size works the other way round: you name a number and the compression is matched to it. The second is useful when a limit is hard, the first when you just want to free up some room without giving up sharpness. How much there is to gain depends on what is inside. Scans and photos shrink a lot; a PDF that came out of Word is mostly text and already compact, so a heavier setting adds little. For a colour contract that was scanned, greyscale often helps more than one step up.
Compression throws away image detail, and it shows first in the places that carry legal weight: a signature, a stamp, a small footnote, a dimension on a drawing. So open the result at one hundred percent and look at the smallest piece of text before you send it. Keep the original as well; sharpness you have given up does not come back, and a second pass over the same file gains almost nothing. With confidential documents it helps that the work happens in your own browser: the file stays on your computer.