Find out what makes it large
Almost all of a large PDF's size comes from images: scanned pages, photos and screenshots. Text takes very little space. A 40-page text document is often under 1 MB, while ten scanned pages can be 20 MB or more.
Compress the images inside the PDF
- Open Compress PDF.
- Choose Medium for a good balance, or Strong for the smallest file.
- Drop in the PDF, check the new size, and download it.
Photos and scans are recompressed and scaled down; text stays sharp and selectable. PDFs that are mostly text are already compact and barely shrink.
Remove pages you do not need
Blank pages, cover sheets and appendices add up. Remove PDF Pages deletes the ones you list and keeps the rest.
Split it into parts
If a file is still over an email limit (Gmail allows 25 MB of attachments), Split PDF can divide it into two or more smaller files by page range.
On a Mac: Preview
Open the PDF in Preview, choose File → Export, and set Quartz Filter to Reduce File Size. It shrinks files a lot, but can make images noticeably blurry, so check the result.