What This PDF Compressor Does
This tool reduces the file size of a PDF by re-compressing the images embedded inside it — typically the largest contributors to PDF file size, especially for scanned documents. Text, fonts and document structure are preserved exactly; only the embedded images are re-encoded at a lower resolution or quality setting. The result is a PDF that looks the same on screen, opens faster, and is far easier to email, upload or store.
Why PDFs Get So Large
A PDF created from a Word document containing mostly text is usually small — often under 1MB — because text is stored efficiently as characters and formatting instructions. A scanned PDF is completely different: each page is essentially a high-resolution photograph of a piece of paper. A single A4 page scanned at 300 DPI in colour can be 2-4MB on its own, so a 20-page scanned contract can easily reach 50-80MB. Compression targets exactly this — the embedded page images — and can typically reduce scanned PDFs by 70-95% with no loss of readability.
Choosing a Compression Level
- Screen (smallest file): reduces embedded images to roughly 72 DPI. Text remains completely readable on any screen or phone. Best for email attachments, portal uploads, and anything that will only be viewed digitally.
- eBook (balanced): reduces images to roughly 150 DPI. Good quality on tablets and screens, with a more moderate size reduction. Suitable for documents shared for digital reading where some zooming may happen.
- Print (largest, highest quality): reduces images to roughly 300 DPI, preserving quality suitable for printing. Use this when the recipient needs to print the document at full quality.
How to Compress a PDF — Step by Step
- Upload your PDF file by dragging it into the upload area or clicking to browse
- Select a compression level — Screen, eBook or Print
- Click "Compress PDF"
- Review the before-and-after file size shown
- Download the compressed file
Compression runs entirely in your browser. Your PDF is never uploaded to a server, which matters for documents containing personal, financial or confidential information — nothing leaves your device at any point.
What If the File Is Still Too Large?
If Screen-level compression still leaves the file larger than you need, a few additional steps can help. Removing unnecessary pages — cover sheets, blank pages, or duplicate scans — with our Remove PDF Pages tool reduces the page count before compressing. For very large multi-page documents, splitting the PDF into sections with PDF Splitter, compressing each section, and sharing them separately or re-merging the compressed sections with PDF Merger can produce a smaller overall result.
How Compression Affects Different Types of Content
Compression's impact varies a lot depending on what's actually in the PDF. Pages that are primarily scanned photographs of text — the most common case for scanned documents — compress dramatically, because reducing the image resolution has little practical effect on text legibility while substantially reducing file size. Pages containing photographs with fine detail or gradients (such as a scanned document that includes a colour photo, or a report with embedded high-resolution images) will show more visible compression effects at aggressive settings — the photo itself may look noticeably softer or show some artefacts at Screen-level compression, even though accompanying text remains crisp. If a document contains a mix of text-heavy pages and image-heavy pages, the overall size reduction will reflect a blend of these effects, and reviewing the compressed result for any image-heavy pages specifically is worth doing if image quality on those pages matters.
Compression as Part of a Document Workflow
For documents that go through several processing steps — scanning, combining with other files, adding page numbers or watermarks, then sharing — where compression fits in the sequence affects the result. Compressing as early as possible (right after scanning, before other operations) means every subsequent step works with smaller files, which can make the whole workflow faster, especially for browser-based tools where processing time often scales with file size. The one consideration is that some operations performed after compression — particularly adding watermarks or page numbers, which involve adding new content to each page — don't meaningfully change the compression of the existing embedded images, so compressing early generally doesn't cause problems with quality for these later steps.
Frequently Asked Questions
Will compression make my PDF unreadable?+
No. Even the highest compression level (Screen) keeps text and images clearly legible on screen. The reduction in DPI is only noticeable if you try to print the document at large sizes or zoom in significantly past 100%.
Why is my compressed PDF only slightly smaller?+
This usually means the original PDF was created digitally (e.g. exported from Word or a website) rather than scanned, and contains mostly text rather than large embedded images. Text-based PDFs are already small and compress less dramatically than scanned documents.
Which compression level should I use for email attachments?+
Screen compression produces the smallest file and is almost always sufficient for email, since most email clients display PDFs on screen rather than printing them. This is the best default choice when you're unsure.
Can I compress a PDF that already has a password?+
Password-protected PDFs typically need to be unlocked first. Use Unlock PDF to remove the password, compress the file, then re-apply protection with Protect PDF if needed.
Is there a limit to how many times I can compress a PDF?+
There's no usage limit, but compressing an already-compressed PDF again won't reduce the size much further and may slightly reduce image quality each time. It's best to compress from the original file whenever possible.