You try to email a PDF and it bounces back: 'attachment too large'. The fix is PDF compression — shrinking the file so it slides through size limits without ruining how the document looks.
What's actually making it big
Most of a PDF's weight comes from images: high-resolution photos, scanned pages, logos at print quality. Text is tiny by comparison. Compression mostly works on those images — reducing their resolution, re-encoding them more efficiently, or stripping unused colour data. The text layer stays crisp. That's why a compressed PDF still reads well.
Lossy vs lossless
Lossy compression throws away some image detail to save more space — fine for emailing, less ideal for print. Lossless keeps every pixel but saves less. Flint's PDF compressor picks a sensible default, but if you're sending to a printer, choose a lighter setting. For email, aggressive compression usually works fine.
When to compress
Email attachment limits are the usual trigger — Gmail caps at 25MB, Outlook at 20MB. Compress before sending, or for documents you want to upload to a portal that complains about file size. If you're merging PDFs into one big file, compress afterwards to keep the total manageable.
FAQ
Will compression make my PDF look worse?
Usually you'd never notice. Aggressive compression can soften photos slightly, but for everyday documents the difference is invisible at screen size. Test before sending anything that needs to look pristine.
Can I compress a PDF too much?
Yes. Pushed too hard, images become blocky and small text turns mushy. Stick to medium settings unless the file is going to email-only use and size is the main worry.
Why does compression do nothing to my PDF?
If the PDF is mostly text with no images, there isn't much to compress. Already-optimised PDFs also resist further squeezing — there's no detail left to remove.
Got an email-busting PDF? Drop it into Flint and you'll usually shave 50-80% off the size in seconds.