Compress PDF Online
Reduce the size of a PDF by rendering its pages at a controlled resolution and JPEG quality. Processing happens in your browser, so your original file is not uploaded to PDFSwift.
Drop a PDF here
or choose a file from your device
Three JPEG rebuilds, not a stream squeeze
Compress PDF opens the file with PDF.js and, for each page, paints a canvas at a fixed scale, then asks jsPDF for a document made of those JPEGs. The configs in the page are exactly {scale:1.7,jpeg:.88}, {scale:1.35,jpeg:.72}, and {scale:1.05,jpeg:.58}. Balanced is the selected default. A 28-page, 22 MB proposal with six photos came back at about 9.8 MB, 4.6 MB, and 2.1 MB on one desktop Chrome run. All three failed a highlight test. That is the mechanism, not a side effect.
There is no uploaded original and no server-side size cap. A large sheet at scale 1.7 is a multi-thousand-pixel bitmap. Twenty of those can crash a tablet. If the status sticks on “Compressing page 4,” the device ran out of memory. Drop a level, move to a desktop, or split the set first. The site is HTTPS. The PDF is not in the request.
| Level | Scale | JPEG | Selectable text |
|---|---|---|---|
| High | 1.7 | 0.88 | No |
| Balanced | 1.35 | 0.72 | No |
| Small | 1.05 | 0.58 | No |
When a picture of the PDF is enough
A mailbox that already bounced
Send the balanced or high sibling. Name it -email. Leave the page-copy master in the project folder for the printer.
A portal at 10 MB
If balanced only moves 22 MB to 19 MB, you are looking at page count, not the slider. Split unused chapters off before you compress again. Re-running small on an already rasterized file mostly softens it.
An invoice that is already a photo of a receipt
Balanced is often enough. Small turns a signature into a gray thumbprint. Zoom the signature before you send.
A file you still have to search
Do not use this page. Split or merge instead, and attach the real PDF, or send a link. Compression is a viewing copy.
Pick a level and look at three spots
- Drop one unlocked PDF. The row shows the size in MB.
- Choose High, Balanced, or Small. Start at Balanced unless the art is a thin vector plan.
- Wait for the page counter to finish. Download the new file. The source name on disk is unchanged.
- Zoom to 200% on a photo, a chart grid, and the smallest footnote. If the footnote is a number someone will retype, raise the level or do not compress.
The measurement notes, including the base64 trap, are in Compress a PDF for email.
Where the time goes
The status line counts pages because each page is a canvas allocation, a JPEG encode, and an add to the jsPDF document. A single wide drawing at scale 1.7 can cost more than thirty text pages at the same setting. If the tab is killed by the browser, you do not get a partial file you should send. Start at Balanced, or split the drawing out and compress the rest. The source file on disk is still the selectable PDF. The download is the one with a new name. Send that, and say in the email that text cannot be copied out of it.
Frequently asked questions
Will I still be able to select the fee table?
No. Every level draws the page to a canvas and builds a new PDF of JPEGs. High, balanced, and small differ by scale and JPEG quality. None of them keep the text layer. If someone must copy a sentence, do not compress that copy.
What are the three settings in numbers?
High is scale 1.7 and JPEG 0.88. Balanced is 1.35 and 0.72. Small is 1.05 and 0.58. There is no fourth mode that squeezes photos and leaves text alone.
Why did a 380 KB letter get bigger?
A text PDF with embedded fonts has little redundant image data. Photographing it adds a bitmap. If the file is already under the mailbox limit and mostly text, keep the original.
An 18 MB file bounced at a 20 MB gateway. Why?
Many mail systems base64-encode attachments, which adds about a third. 18 MB of PDF can become 24 MB on the wire. Aim nearer 12–14 MB of PDF bytes for a 20 MB mailbox.
Is the compressed file stored on a server?
No. The render loop stays in the tab. HTTPS delivers the page. There is no PDFSwift copy to delete. Your download folder is the only copy, and the source file is not overwritten unless you replace it.
Can I compress a locked PDF?
Not until PDF.js can open it. Unlock a permitted copy first. Locking afterwards rasterizes again. Stacking unlock, compress, and lock is three photographs of the same pages.