Your design firm has just sent over a 47-page PDF brand book. It's gorgeous. It's also 84 MB, and the email server rejects anything over 25. Compression is the lever you reach for. This guide explains what's actually happening when you compress a PDF — what gets smaller, what stays the same, and how much you can realistically shave off — using Flint's Compress PDF tool.
What compression actually does to a PDF
A PDF is a container. Inside that container sit text, vector graphics, embedded fonts, raster images, and metadata. Most of the bytes — by a huge margin — come from the images. So compressing a PDF is mostly about doing three things to those images, and a few small things on the side.
- Image downsampling. A photograph embedded at 600 DPI looks great in print and identical to your eye at 150 DPI on a screen. Compression drops the pixel density on raster images to a sensible screen-viewing target. This alone is where most of the savings come from.
- JPEG re-encoding. Many PDFs ship images as near-lossless JPEGs or even uncompressed bitmaps. Re-encoding them at a sane quality factor — somewhere between 65 and 85 — drops file size dramatically with barely visible quality loss.
- Metadata and unused object stripping. PDFs collect cruft: deleted-but-not-removed objects, embedded thumbnails, unused fonts, XMP metadata, document history. Stripping it doesn't shave gigabytes, but a few hundred kilobytes is worth having.
- Object stream re-packing. Modern PDFs can pack many small objects into a single compressed stream. Older PDFs often don't. Re-packing closes the gap.
What compression doesn't do: it doesn't flatten your text into images, doesn't mess with vector graphics, and doesn't alter the page count or layout. Selectable text stays selectable. Searchable text stays searchable. The PDF still opens in every reader.
How to compress a PDF with Flint
The whole flow is one page, three clicks. No install, no signup to try, no shuffling files between desktop apps.
Upload your PDF
Pick a quality level
Compress and download
What to do with your compressed PDF
The compressed file lands in the Flint editor, same as any other PDF. From there:
- Email it. A 12 MB PDF clears nearly every mail server in the world. If you're still over the limit, consider splitting the document instead with Split PDF and sending chunks separately.
- Sign it. Use Sign PDF to drop a signature on the compressed version. Compression before signing keeps the audit trail cleaner — the signed file is based on the small one.
- Lock it. Password Protect PDF encrypts the compressed result with AES-256 — useful when you're emailing sensitive material.
- Combine it. Merging a compressed PDF into a larger pack with Merge PDF is a clean way to keep the final bundle lean.
Other ways to compress (and when to use them)
Compression is built into a few places. The right tool depends on what's already in front of you.
macOS Preview
On a Mac, open the PDF in Preview, then File → Export → Quartz Filter → Reduce File Size. Free and built-in. Catch: Apple's default filter is aggressive — text-heavy PDFs sometimes come out blurrier than you'd like. Fine for casual use, not great for anything you'd send to a client.
Adobe Acrobat
If you already pay for Acrobat, its Optimize PDF dialog is excellent — exposes granular controls over downsampling and font subsetting. It's also $20 a month and only useful if you're sitting in front of the desktop app.
Ghostscript on the command line
For developers and sysadmins, Ghostscript will compress a PDF with a one-liner. Powerful, scriptable, totally inscrutable to anyone not comfortable in a terminal. We use it under the hood for parts of our pipeline.
Flint (the case for it)
Flint sits where the others fall short: any operating system, no install, no subscription to a 300 MB desktop app. The compressed PDF lands in the editor so you can keep working — sign it, redact it, merge it — without bouncing between tools. Bookmark Compress PDF if you do this more than once a month.
Tips for getting the smallest sensible file
- Start with medium. It hits the sweet spot for 90 percent of real-world PDFs. Only drop to low if medium isn't small enough.
- Compress once, not repeatedly. Re-compressing an already-compressed PDF gives diminishing returns and can visibly degrade images. If the first pass isn't enough, go back to the original and pick a more aggressive setting.
- Redact before you compress, not after. If you're removing sensitive content with Redact PDF, do that first — redaction may add data, compression then cleans up.
- Scanned PDFs benefit the most. A 200 MB scan of a contract often drops to 15 MB at medium without anyone being able to tell the difference. If your file is mostly scanned pages, expect dramatic savings.
- Vector-heavy designs benefit the least. A PDF exported from Illustrator that's mostly vector art will barely shrink — there's little to compress. If it's still huge, the export settings are the problem, not the PDF.
Compressing a PDF: frequently asked questions
Will I lose quality?
At medium, almost imperceptibly. At low, you'll see slightly softer images if you look closely, particularly on photographs. Text stays sharp at every quality level — it's not affected by image compression.
How much smaller will my file get?
Image-heavy PDFs (brochures, scans, presentations with photographs): expect 40-70 percent reduction. Text-heavy PDFs (contracts, reports, essays): usually 10-20 percent. The compression ratio shows in the editor after processing so you can decide whether to keep or retry.
Is the compression reversible?
No — compression is lossy. The downsampled images can't be restored to their original resolution. Always keep your original file somewhere safe if you might need the high-quality version later. Your files in Flint stay in your account, so the original is still in My Documents too.
Does it work on password-protected PDFs?
Only if you have the password. Encrypted PDFs need to be opened before they can be processed. Once decrypted, you can compress and then re-encrypt with Password Protect PDF if you still need protection.
What's the maximum file size?
Flint Pro accepts files up to 250 MB.
Will it still be searchable after compression?
Yes. Text is left alone by the image-focused compression. Selectable text stays selectable, searchable text stays searchable. If your file is a scan that's never been OCR'd, it won't be searchable before or after — you need OCR for that, separately.
Can I compress multiple PDFs at once?
Right now Flint compresses one file at a time — batch compression is on the roadmap. If you need to process a stack, run them through one after another; each finishes in seconds.
Ready to compress?
Drop a PDF into Flint's Compress PDF tool and you'll have a smaller version in seconds. Most people pick medium and move on. The rest of the toolkit — sign, merge, split, redact — is one click away if you need it next.