PDF Compressor
Compress a PDF in your browser by re-encoding its embedded JPEG images at a lower quality and restructuring the file with object streams, no upload needed.
PDF Compressor — Shrink a PDF entirely in your browser: it re-encodes embedded JPEG (DCTDecode) images at a lower quality and re-saves the document with object streams to drop redundant structure. The file is parsed with pdf-lib and re-encoded with the Canvas API locally, so it is never uploaded anywhere. PDFs built mostly from scanned pages or photos shrink the most; text-and-vector documents change little.
What is PDF Compressor?
A free online PDF compressor that reduces PDF file size right in your browser. It targets the two things that bloat a PDF: heavy embedded raster images and redundant document structure. Choose a Low, Medium, or High quality level, and the tool re-encodes the embedded JPEG images at that quality with the Canvas API and re-saves the whole document with object streams turned on. Office workers emailing reports, students uploading assignments under a size cap, and anyone hitting a PDF upload limit can drop a file in and get a smaller one back. Because both the parsing (pdf-lib) and the image re-encoding (Canvas) run locally, the PDF is compressed without ever leaving your device.
How to use PDF Compressor
- Drop a PDF onto the dropzone, or click it to browse and pick a PDF from your device.
- Pick a quality level: Low for the smallest file, Medium for a balance, or High to keep images untouched and only restructure the document.
- Watch the Original, Compressed, and Saved stats update automatically a moment after the file loads — no extra button press to compress.
- Check the first-page preview to confirm it is the right document; click it to enlarge.
- Click Download to save the compressed PDF, or use Reset to clear and start over with another file.
Examples
Shrink a scanned PDF before emailing it
Drop a scanned multi-page PDF made of photographed pages and pick Medium. The embedded JPEG images are re-encoded at lower quality, the Compressed stat drops well below the Original, and Saved shows a negative percentage like -55%. Download saves it as document-compressed.pdf.
Restructure a PDF without touching image quality
Pick High on a report that is mostly text and charts. Images are left exactly as they are, and the document is re-saved with object streams. The size may shrink only slightly (or show a small + if it was already optimized), but page rendering is unchanged.
Squeeze a photo-heavy portfolio to the smallest size
Drop a PDF full of full-page photographs and pick Low. Each embedded JPEG is re-encoded at a much lower quality, giving the largest size reduction at the cost of some visible image detail.
Frequently asked questions
- How does the compression actually work?
- Two ways. The document is always re-saved with object streams enabled, which removes redundant structure, and for Low and Medium quality the embedded JPEG (DCTDecode) images are decoded and re-encoded at a lower quality with the Canvas API. High skips the image step and only restructures.
- Why did my PDF barely get smaller?
- Most of a PDF's size usually comes from raster images. A PDF that is mostly selectable text and vector graphics has little for the tool to re-encode, so the savings are small. The biggest reductions come from scanned or photo-heavy PDFs at Low or Medium quality.
- Will compressing reduce the image quality?
- At Low and Medium, yes — embedded JPEG images are re-encoded at a lower quality, which is what shrinks the file. High leaves all images untouched and only restructures the document, so visual quality is preserved.
- Why did the compressed file come out the same size or larger?
- If the images were already well compressed, re-encoding can match or exceed their size; in that case the tool keeps the original image. The Saved stat shows ± or a + percentage. Picking a lower quality, or accepting that an already-optimized PDF can't shrink much, are the options.
- Is my PDF uploaded to a server?
- No. Everything runs 100% client-side in your browser — pdf-lib parses the file and the Canvas API re-encodes the images. Your PDF is never uploaded, sent, or stored anywhere, so it works even offline once the page has loaded.
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