Compress PDF

Not the lossless copy, which changes how the file is packed, not what is on the pages. Deep image compression is lossy: Extreme gives up the most detail, High quality the least, and Balanced is the default. Grayscale removes all colour from the copy; your original keeps it. Afterwards our server checks that the result opens as a PDF and, if it can count them, that no pages went missing; nothing compares how the images look, so open the result before deleting your original.

Not by default. An optional, clearly labeled step uploads the file to a secure server — only when you start it, and only after the page confirms a server is available. Here that step is the “Compress images on our server” button: the analysis and the lossless copy both run in your browser, and the button is shown only once the panel has confirmed a secure server is available.

Yes, on the deep step. In the “Deep image compression (secure server)” panel, choose a “Target size”: “100 KB”, “200 KB”, “500 KB” or “1 MB”, or “Custom” for a number of KB. Our server starts at your Quality setting and steps down, as far as Extreme, until the file fits, and returns the highest-quality version that does; the panel then says, for example, “Now 184.0 KB — under your 200 KB target.” A lower setting usually makes a smaller file but not always, so each setting it tries is measured; if none fits, you get the smallest file it made and the panel says it is above your target; tick “Grayscale” or split the file and try again. How small a file can get depends on how much of it is images: a mostly-text PDF may hardly shrink at all. “No target” is the default and runs exactly as before. The step uploads your file to our server, and each run starts from your original.

A mostly-text file that is already well packed has little to remove, so the page says “This PDF is already lean” and the Lossless result tile may read “No change”. Without Grayscale, our server never returns a file bigger than the one you sent; if it cannot shrink it, it says so and offers no download. With “Grayscale” ticked the gray copy is offered even when it did not get smaller, because your original is still in colour, and the panel says it did not get smaller.

A PDF that needs a password to open is refused with a request to unlock it with its password first. One that opens freely but restricts printing or editing cannot be repacked in your browser, so the page offers our secure server's deep step for it instead; our server may not be able to process an encrypted file, and says so if it cannot. In a batch of several files, such a file fails with a note to compress it on its own. An unreadable file gets an error instead of a download. On the deep step our server rejects a result with fewer pages than the original; if it cannot count the original's pages, it returns the smaller file with a warning that it was not checked page-for-page.

No. Both the lossless copy and the deep step write the file out anew instead of appending to it, and a signature covers the exact bytes it was applied to, so it stops validating. Compress before signing, or keep the signed original.

Only then does the file leave your device. Inputs are wiped when the job finishes, the download link stops working after 60 minutes, and stored copies are erased by a daily storage rule.

Up to 100 MB per file.

Not in your browser: that step re-saves the same pages, packed more tightly, and every page looks exactly as before. Only the optional secure-server step changes quality — it lowers the resolution of images sharper than the level you pick: Extreme (72 DPI), Smaller (96 DPI), Balanced (150 DPI) or High quality (300 DPI). Its Grayscale switch is off unless you tick it: Turns every colour on the pages — pictures, text and drawings — into shades of gray. Our server checks the result and refuses it if a picture is still in colour.

That depends on what the file holds, so no figure is promised in advance. The in-browser step measures the exact saving before you download, and offers the download only when the file got smaller. When it saves little and images make up 40% or more of the file, it points you to the secure-server step, which is where the images themselves are made smaller.