Compress large PDF files

What a browser tab is allowed to use

The engine runs inside the tab, so the tab's memory budget is the real ceiling, not any rule in the tool. An iPhone 16 Pro class phone with 8 GB of RAM on iOS 26.6 gives a tab 2 GiB, and a 300 page run fits inside it. Desktop browsers have more room: the largest public file in the run, 38.4 MB, compressed in one pass in a desktop browser. The compressor is free and runs in the tab, so a large file needs no upload.

A second limit binds before memory does on any single page. A canvas tops out at 8192 by 8192 pixels, exactly 67,108,864 of them. One row more comes back blank with nothing reporting a failure. The largest page in the test corpus at 150 dpi is 9.9 million pixels, 15% of that cap, so ordinary pages are nowhere near it.

Page count is the number that matters

Megabytes are a bad predictor. A 60 MB file that is 12 pages of photographs is easy. A 30 MB file that is 900 scanned pages is the hard one, because the raster method walks every page.

That walk was measured. On the same phone, a 300 page run at 150 dpi finished all 300 pages in one tab without a kill, at a median of 671 ms a page, and the per-page cost drifted up only 17% across the whole run. The memory comes back between pages, so a long document runs page after page without piling up.

How long it takes

An ordinary document takes a couple of seconds: the median case in the public run finished in 1.7 seconds. A long scan takes longer, because the raster method renders every page, at roughly two thirds of a second a page on a phone and faster on a laptop.

What to close before you start

Three habits stop a long run from failing halfway.

• Give the tab room. Close the other heavy tabs, especially anything holding video or a map, and do the job in a window with nothing else loaded. On a desktop that is usually enough for any document you are likely to have.
• Do not reload the page while it is working. The document lives in the tab memory and a reload throws it away, so a long run starts again from the beginning.
• Watch the reported size rather than the clock. The result shows the size it reached, and on a long document that number tells you whether to split.

When the file will not go small enough

Try the size first. The large file page and a 10 MB target both run the same engine, and the top tenth of the public run gave back 97.1% or more of the source bytes.

If the cap is an ordinary attachment limit, the 1 MB page covers the most common one. If it is a government upload field, the 150 KB page says how many pages fit under it, and a long document goes in parts.

If it still does not fit, split rather than squeeze. A 400 page manual sent as four 100 page files reaches the other end. The same manual crushed until it fits one mail attachment arrives unreadable. Organize pages cuts a document into parts without rebuilding it.

And check what is actually heavy before assuming compression is the answer. The general guide covers how to tell a scan from a text document in five seconds, which decides everything else. The compress hub lists the rest of the cluster.