Compress PDF — Reduce PDF File Size Online, Free

Guide: how to compress a PDF file size

How to compress a PDF file size, step by step

• 1. Open the PDF in the tool above. Drag it into the box or tap to choose it. It stays on your device.
• 2. Choose a level. Start with Recommended; it suits most scanned documents. Use Light when the PDF will be printed, and Strong only when a portal's limit forces it.
• 3. Compress and compare. The tool shows the old and the new size side by side.
• 4. Check the result. Open the new PDF and zoom in on the smallest text on each page. If it is still readable, you are done.
• 5. Too big still? Try the next level, or remove pages that are not needed, then compress again.

How much smaller will the PDF get?

It depends on what is inside the file. A PDF made from phone photos or a high-resolution scan is mostly large images, and those shrink a lot, often to a fraction of the original size, because each page is redrawn at a sensible resolution. A PDF that is mostly typed text, such as a bank statement or a document exported from Word, is usually small already. Turning its text into images can even make it larger, so for those files use one of the other methods below.

For reference, a PDF page is measured in points, 72 to the inch. At Strong the tool draws each page at 72 dots per inch, at Recommended about 108, and at Light about 144. Normal printed text stays readable at around 100 to 150 dots per inch, which is why Recommended is the usual choice and Strong can make small print hard to read.

Other ways to compress a PDF, especially text documents

• Export again from the source: if you made the PDF in Word, Google Docs or PowerPoint, export it again and choose the smaller or "minimum size" option. This keeps the text sharp and selectable.
• On a Mac: open the PDF in Preview, choose File, Export, and pick the "Reduce File Size" Quartz filter. It works well on image-heavy files but can lower quality noticeably.
• Adobe Acrobat: the paid versions have a "Reduce File Size" and an "Optimize PDF" command that compress images while keeping text as text.
• Fewer pages: many portals only need the relevant pages. Removing blank, duplicate or cover pages is the easiest saving of all.
• Rebuild from images: for scans, convert the pages with PDF to Image, crop the margins, compress each image to a target size and combine them again. Our guide to combining photos into one PDF under 100 KB walks through it.

What the three levels do

The tool opens your PDF with pdf.js, draws every page onto a white canvas, saves that page as a JPG image, and then builds a new PDF with jsPDF in which each page has the same physical size as before. The levels change two things, the resolution of the page image and the JPG quality:

• Light: pages rendered at 2x and saved at quality 0.82. An A4 page becomes about 1190 by 1684 pixels.
• Recommended: 1.5x at quality 0.70, about 893 by 1263 pixels for A4.
• Strong: 1x at quality 0.55, about 595 by 842 pixels for A4.

Good and poor candidates

The method works well when pages are already pictures: documents scanned with a phone app or office scanner, certificates scanned at high resolution, brochures full of photos, and PDFs made from camera photos with Image to PDF. It works poorly on PDFs that are mostly typed text, such as bank statements, invoices from accounting software or files exported from Word. Those are usually small already, and turning their crisp text into images can make them larger and blurrier.

The result screen shows the original and new sizes. If the new file is not smaller, it says so, but the download button still offers the new file; in that case, keep your original.

What you lose in the process

Every page becomes a single image. Text is no longer selectable or searchable, so you cannot copy an account number or search for a name. Hyperlinks, bookmarks and fillable form fields are removed. A digitally signed PDF loses its signature, because the file is rebuilt from page images. Do not use this tool on documents whose signature or text needs to be verified; send the original instead. Password-protected PDFs cannot be opened.

Meeting a portal's size limit

Admission, scholarship and recruitment portals usually set a maximum file size for each document. Try Recommended first, then open the result and zoom in on the smallest print. If the file is still too large, try Strong and check again; at 1x, small text can become hard to read. If Strong is not readable, upload only the pages that are actually required, or rebuild the document: convert the pages with PDF to Image, crop away the margins with the Crop tool, reduce the images with Bulk Compress, and combine them again with Image to PDF.

Speed and privacy

All of this happens on your device, and the PDF is never uploaded, which matters for documents such as salary slips, ID cards and medical reports. The progress message shows which page is being processed. Long documents take time because each page is drawn and encoded in turn, and they work better on a computer than on a phone.

Checklist before you submit

• Keep the original PDF; the compressed copy cannot be turned back.
• Read the smallest text on every page of the result.
• Check that the page count matches the original.
• Do not compress signed or legal documents that someone will need to verify.
• If a portal wants separate files for each document, compress each PDF on its own instead of one combined file.
• Try Light first if the document will be printed.

Related guides

• Photo and Signature Size for Online Forms: KB, Pixels and Format
• How to Compress Images Without Losing Quality (and Reduce Size in KB)
• Best Free Online Image Tools for Students