How to Compress a PDF File
Upload your PDF, set the quality slider, and download a smaller file — that's it. Behind the scenes the compressor does two things: re-encodes the images inside your PDF as JPEG at the quality you chose, scaled down for the screen, and removes duplicate and unused objects that bloated the file. In our test at the default setting of 75, a scanned bank statement shrank by 46%, a photo PDF by 62% and a 1,200-page digital text document by 12%; at 25 the same files shrank by 80%, 88% and 43%.
PDFs collect waste over time. Each edit cycle can leave duplicate resources and unused objects behind. Compression cleans this up — similar to emptying a cache. The content you care about (text, pages, bookmarks, links) stays intact; the leftovers get stripped.
The slider trades quality for size. At 100 nothing is re-encoded and only redundant data goes — use it for documents you'll print. The default 75 is the sweet spot for email and web. Lower values make smaller files, good for quick previews where top quality doesn't matter. See the table below for the measured numbers.
Why Reduce Your PDF File Size?
A PDF that's too large creates real problems. Email servers reject attachments over 10–25 MB. Upload forms time out. Recipients on slow connections can't download your file. In our test a 12.9 MB scanned statement became 7.0 MB at the default setting and 2.6 MB at 25 — small enough to attach to any email, upload in seconds and download fast on mobile data. If you regularly send PDFs to clients, colleagues or submission portals, making them smaller saves everyone frustration.
Beyond email, smaller PDFs load faster on websites, consume less storage, and reduce bandwidth costs. A 500 KB PDF opens almost instantly on mobile. A 10 MB one makes the user wait. For high-traffic sites, document portals, or learning platforms, compressing PDFs before upload measurably improves the experience. Organizations with thousands of documents save substantial storage through systematic compression — and the savings compound.
When You Need to Make a PDF Smaller
Email is the #1 reason people compress PDFs. Proposals, contracts, reports — when your quarterly deck exceeds the attachment limit, compression delivers it. HR teams compress policy documents for company intranets. Marketing teams reduce product catalogs before web upload. Legal teams shrink case files for electronic filing systems with strict size caps.
Students and educators hit upload limits constantly. That 50 MB scanned textbook chapter needs to fit a 10 MB portal cap — compression makes the difference between submitting on time and fighting the system. Researchers compress image-heavy papers for journal portals. Designers reduce PDF portfolios for email delivery without sacrificing review-quality visuals.
Archives and records management depend on compression. Historical document scans add up to terabytes, and in our test scanned pages shrank by 46–99% at the default setting. Real estate agents compress photo-heavy property brochures. Insurance companies shrink claim documentation for digital record systems. Any workflow that moves PDFs around benefits from smaller files.
Key Features of Our PDF Compressor
- One slider, 10 to 100: 100 removes only redundant data, lower values re-encode the images
- Preserves text searchability, hyperlinks, bookmarks, and form fields during compression
- Re-encodes embedded images as JPEG at the quality you choose and scales them down
- Removes duplicate and unused objects left behind by editing
- Processes multi-page documents and scanned PDFs efficiently
- Files up to 100 MB without an account, 500 MB with Premium and 1 GB with Premium Plus
What Happens During Compression
The biggest space saver is image re-encoding. Scanned documents and photo-heavy PDFs often contain images at print resolution, sometimes stored without lossy compression. The compressor re-encodes them as JPEG at the slider quality and scales them down — to 88% of their pixel size at 75, 63% at 25. In our test this took a scanned bank statement from 12.9 MB to 7.0 MB at 75 and to 2.6 MB at 25.
Beyond images, the optimizer removes duplicate resources and unused objects that accumulated through editing. It does not subset fonts or strip document metadata, so a file opens and reads exactly as before, just leaner where the waste was.
Which Slider Value Should You Choose?
The right slider value depends on what you're doing with the file:
- 100 (lossless) — 100 — lossless: only duplicate and unused objects are removed, images stay untouched. In our test a scanned PDF stayed the same size and a digital text document shrank by 8–16%. Use it for documents you'll print, archive or need at full fidelity.
- 75 (default) — 75, the default — images re-encoded as JPEG at quality 75 and scaled to 88% of their size. In our test: a scanned bank statement 46% smaller, a photo PDF 62% smaller, a digital text document 12% smaller. The right choice for email attachments, web uploads and most everyday use.
- 25 — 25 — the smallest file, acceptable on screen: JPEG quality 25 and images scaled to 63%. In our test scans shrank by 80–100%, a photo PDF by 88% and a digital text document by 43%. Use it for quick internal previews or when storage space is the priority.
What Each Slider Value Does
The slider sets the JPEG quality for the images inside the PDF and how much they are scaled down; 100 skips the images and only removes redundant data. The numbers below come from our test on six PDFs: two scans, a photo PDF and three digital documents.
| Slider | Size Reduction | Quality | Best For |
|---|---|---|---|
| 100 (lossless) | 0% on scans, 8–16% on digital text (our test) | Identical | Printing, archival copies |
| 75 (default) | 46–99% on scans, 62% on photos, 8–12% on digital text (our test) | Hard to tell apart on screen | Email attachments, web uploads |
| 50 | 66–99% on scans, 79% on photos, 8–22% on digital text (our test) | Slightly softer images | Large scans that must fit an upload limit |
| 25 | 80–100% on scans, 88% on photos, 11–43% on digital text (our test) | Visibly softer, readable on screen | Quick previews, storage optimization |
FileConvertLab vs Adobe Acrobat for PDF Compression
Adobe Acrobat Pro is the established option for PDF compression — and it does the job well. But it requires a subscription, software installation, and a fairly heavy desktop application. If you're already paying for Creative Cloud, Acrobat makes sense. If you just need to compress a PDF occasionally, installing a multi-gigabyte suite is overkill.
FileConvertLab compresses PDFs without an install and without a subscription to start, for the same compression result. Upload, pick a level, download. It's faster for one-off tasks and works on any device including phones and tablets. For teams processing documents in bulk, the PDF compression API handles programmatic compression without per-seat licensing costs.
How to Get the Best Compression Results
Match the slider to your goal. For email and web, the default 75 is the sweet spot — image-heavy files shrink by roughly half or more and still look good on screen. For printing or archiving, use 100. For quick internal previews, 25 is fine. Always open the compressed file and check it at 100% zoom before sending — text should be sharp, images acceptably clear.
Compress at the end of your workflow, not in the middle. Each compression pass permanently discards some data — keep an uncompressed original and compress a copy for distribution. Before compressing, remove pages you don't need with Split PDF. If you're combining multiple documents, merge them first, then compress the combined file — you'll get better results than compressing each separately. For scanned documents, scan at 150-200 DPI initially rather than 600 DPI and compressing afterward.
Which PDFs Compress Best?
Image-heavy PDFs see the biggest results: scanned documents, photo albums, brochures and presentations with embedded images. In our test at the default 75, an 11.6 MB scanned invoice shrank by 99%, a scanned bank statement by 46% and a photo PDF by 62%. The compressor re-encodes raster images as JPEG at the chosen quality and scales them down; vector graphics and text are not touched.
Text-based PDFs with few images compress far less, because text streams are already compact: in our test a 1,200-page digital document lost 12% at 75 and a report with tables 8%, mostly from removing duplicate and unused objects. Fonts are not subsetted and vector graphics are kept as they are.
Related PDF Tools
- Merge PDF — combine multiple PDFs before compressing for a single optimized file
- Split PDF — extract pages before compression if you only need part of a document
- PDF to Word — convert compressed PDF to editable Word format
- PDF to JPEG — extract pages as images for web use
- OCR PDF to Word — extract text from scanned PDFs after compression