Compress a PDF

Compression works by re-encoding the images a scanned page is made of, at a lower resolution and quality. That is the only lever that meaningfully changes PDF size in a browser: re-saving a file, stripping its metadata or tidying its internal structure all make essentially no difference. Because the method turns pages into images, it is the wrong tool for a document that already contains real text — that file would get larger, not smaller, and lose its searchable text. The tool checks first and tells you rather than doing it anyway.

Why did it refuse to compress my file?

It contains selectable text. Compressing would destroy that text and usually produce a bigger file, so the tool stops and explains instead.

How much smaller will my scan get?

It depends on the scan. The tool reports the actual before and after sizes rather than a promised percentage.

Will the text still be searchable?

No. Compressed pages are images. If you need searchable text, run OCR after compressing.