Compress PDF to 8MB

Eight megabytes holds a lot: a fifty-page greyscale scan, a thirty-page colour scan, or a couple of hundred pages of text. When a document of ordinary length runs past it, something inside it is unusually expensive, and it is normally possible to say what.

Where the 8 MB limit comes from

Eight is a round number in binary, which is why it shows up in systems written by people who think in those terms: document stores, submission systems, versioning platforms. It also appears as a deliberate margin. A team whose mail gateway refuses attachments over 10 MB will often publish 8 as the working limit, leaving room for the encoding overhead that a mail attachment picks up on the way.

How the tool hits 8 MB

What fits in 8 MB, and what does not

Text is almost free at this scale. A page of type costs about forty kilobytes, so two hundred pages of it still fit. Greyscale scanning costs a hundred and thirty a page and colour about two hundred and forty, and a full-page photograph at print resolution can cost several times that on its own.

When it cannot reach 8 MB

Some documents will not fit legibly, and the tool says so rather than pretending. When the result line reports a miss, three moves usually solve it:

• Split first. Use Split PDF to break the file into parts and compress each. Most portals accept several attachments even when each one is capped at 8 MB.
• Rescan the source. A fresh 150 dpi greyscale scan compresses far better than a colour scan that has already been through one compressor. Every pass costs quality, and the first pass should start from the cleanest source.
• Check the real limit. Portals sometimes state one number and accept another. Read the fine print, or try a slightly larger file before compressing harder than you need to.

Find the expensive pages

Weight in a PDF concentrates. A forty-page report where thirty-eight pages are text and two carry full-resolution photographs is not a heavy document; it is a light document with two heavy pages in it. Compressing the whole file spreads the loss across all forty, softening thirty-eight pages that were never the problem, to save bytes that were only ever in two of them.

Finding the heavy pages does not need a special tool. Split the document into halves with Split PDF and look at the two file sizes. The heavy half is obvious, and three or four rounds of halving narrow it to a page or two. It takes about two minutes and it tells you something no compression setting can: what is actually in your file.

Once you know, the fix is usually specific. A photograph pasted from a phone camera is a twelve megapixel image being displayed at the size of a postcard, and it can lose nine tenths of its pixels without any visible change. A scanned signature page at 600 dpi is doing the same thing. A screenshot saved as a lossless image is a third case, and the one where re-saving as a JPEG makes the largest difference. In each case the right move is to replace the offending image and rebuild the page, rather than to squeeze the document.

If that is more work than the situation deserves, the tool above will get the file under the cap regardless. It steps the images down in resolution first and leaves text untouched, so even the blunt approach costs less than it might. But when a document has to stay presentable, two minutes of halving beats any amount of compression.

Where people use the 8 MB target

Why this runs in your browser

Inspection records, audit files and case documents are exactly the material that should not be uploaded to a third party in order to be made smaller. Everything on this page runs on your own machine, so the question does not arise.