How to Compress a PDF
Almost every oversized PDF is oversized for the same reason: images. Text is remarkably light — a hundred pages of it might be a megabyte — while a single photograph from a modern phone can be five. Scanned documents are the extreme case, since every page is a full-resolution picture of a sheet of paper.
Compressing re-encodes those images at a resolution that still looks right on screen and in print, without touching the text. This guide covers running the compression, deciding whether the result is good enough, and what to do when a file simply refuses to get smaller.
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Open the toolWhen you need to compress a PDF
- Getting an attachment under a mail server limit, which is often 10 or 25 MB.
- Uploading to a portal that rejects anything above a few megabytes.
- Publishing a document for download where a heavy file means a slow page and impatient readers.
How to compress a PDF step by step
Open the Compress PDF tool
Go to the Compress PDF page. The process runs in the browser, with nothing to install and no account required.
Upload the document
Drag the PDF onto the upload area or select it from the dialog. Several files can be queued together.
Run the compression
Start the process and let the images inside the document be re-encoded. Large scanned files take the longest, because there is the most to work on.
Compare the sizes
Look at the size of the result against the original. Text-heavy documents shrink modestly, image-heavy ones often lose most of their weight.
Check the quality before sending
Open the compressed file and read a page of small print at 100% zoom. If the text is comfortable and photographs look acceptable, the file is ready to go.
Common problems and how to fix them
The file barely got smaller
It was probably already efficient — a text document with few images has very little to remove. If it is still too big, split it into parts with Split PDF and send them separately.
Photographs look soft afterwards
Compression reduces image resolution, and that is the whole mechanism. When photographic quality is the point, send the original file through a file-sharing link instead of squeezing it into an attachment.
A scanned document is still enormous
Scans made at 600 dpi carry far more detail than any screen shows. Rescanning at 200–300 dpi produces a dramatically smaller file, and for text pages a grayscale scan is smaller still.
Compressing versus splitting or sharing a link
Compress first — it is the least disruptive option. The recipient still gets one complete document, and for scans and photo-heavy files the size reduction is usually more than enough to clear an email limit.
If the file is still too large, splitting keeps everything readable but breaks the document into parts, and a share link keeps full quality but requires the recipient to download from somewhere. Compress for convenience, split for stubborn email limits, share a link when quality genuinely cannot be sacrificed.
常见问题
Will compression make the text blurry?
No. Text is stored as text and is left alone. Only images are re-encoded, which is where the size savings come from.
How much smaller will my file get?
It depends entirely on the content. Scanned and photo-heavy documents often shrink by more than half; a plain text document may barely change.
Can I compress the same file twice?
You can, but the second pass gains little and costs image quality. One pass is the sensible limit.
Is the original file changed?
No. A new compressed document is generated for download and your original stays as it is.
What if it is still too large?
Split the document into parts, or convert scanned colour pages to grayscale, which removes a great deal of data.
Is there a size limit?
Files up to 100 MB are accepted, with no daily limit, no registration and no watermark.
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