Everyday

Compress a PDF

Pick the PDF up, hold ⌥, let go toward Compress.

What makes this different

Most PDF compressors rasterise. Every page is rendered to an image, the images are JPEG-compressed, and a new PDF is built out of the pictures. The file gets dramatically smaller, which is why the number looks so impressive.

What you lose: selecting, copying and searching text; screen readers, so the document stops being accessible; crisp text when zoomed; and any chance of getting it back.

Arazio does not do that. It subsets the embedded fonts — cutting each one down to the characters the document actually uses — and shares streams that appear twice. The words stay words.

And then it checks

Subsetting is not universally safe. A PDF refers to glyphs by number, and in some documents the character codes reach glyphs in a way that a subsetter can get wrong. When that happens the file still opens, still reports all its text to a search, and draws the wrong letters.

So Arazio renders both documents and compares them pixel by pixel. If anything moved, it throws its own work away and gives you back the file you started with.

This is why compressing can never quietly ruin a document, and also why it takes a second or two on a long one.

How much smaller

It depends entirely on what is inside.

A text document from Word, Pages or Excel — often 20–30% smaller. One 31-page report here went down 27% with every page rendering identically; it had no images at all, and was carrying ten typefaces with 4,551 glyphs for a document that used 85 distinct characters, including Arial embedded twice.

A scan or a photo album — every page is already a picture, so the saving comes from re-encoding those images, and how much depends on how they were made.

An already-tight PDF — nothing. If a document was made properly, with subset fonts and compressed images, there is nothing left to take. Arazio says so in those words and returns the original rather than a copy that is somehow larger.

Checking it worked

Open the result and try to select a line of text.

If you can highlight individual words, the text survived. If the whole page highlights as one block, or nothing highlights, it was rasterised — by whatever produced it. Do that check before deleting an original.

Why Preview often makes it bigger

macOS has File → Export → Quartz Filter → Reduce File Size in Preview. It is free and worth trying on a scan, where it downsamples images to 72 dpi.

On a text document it frequently produces a larger file. It has nothing to take from a page of words, and the re-encode adds overhead. That is the tool meeting a file it has no answer for, not you doing it wrong.