CompressaPDFto1MB

What 1 MB realistically means

1 MB is the friendliest of the common limits. Most scans reach it on medium quality with no visible change at all, which means you rarely have to trade legibility for it.

How to get there

• Medium quality. Check the result before touching anything else — this alone clears 1 MB for the majority of documents.
• If it is close but not under, greyscale usually finishes the job.
• Crop before dropping quality. A scanner border can be a surprising share of a file, and trimming it costs you nothing on the page.

Because the target is generous, this is the case where it is worth keeping the document sharp — resist going to low quality for the sake of a margin you do not need.

If it still will not fit

There are three moves left, in order of how much they cost you:

• Greyscale. A colour scan of black text carries three channels describing grey paper — dropping them is often a third of the size, at no cost to legibility.
• Crop. A scanner's black border and wide margins are bytes spent describing nothing. Trim them, then compress.
• Split. If the limit is per file rather than per submission, send the document in two parts. This is almost always allowed and almost never tried.

What does not help is compressing twice. The second pass re-renders an already-rendered page: you lose quality and save almost nothing.

Why the file was so large to begin with

A PDF from a word processor is a few kilobytes a page, because it stores text as instructions. A scan stores a photograph — an A4 sheet at 300 DPI is roughly 8.7 million pixels — and a scanner that saves those without much compression produces several megabytes per page.

That is the whole story behind almost every oversized PDF. It is not corruption and nothing has gone wrong; it is eleven photographs in a wrapper.