What's actually taking up space in a large PDF
In the overwhelming majority of oversized PDFs, the culprit is images. Usually scanned pages saved at a resolution meant for printing (300 DPI or higher) even though the file will mostly be read on a screen. Text itself, when a PDF is generated from a word processor rather than scanned, takes up almost no space at all. A whole page of typed text might be a few kilobytes, while a single scanned image-based page can be several megabytes on its own.
This is why "compress this PDF" doesn't mean the same thing for every file. A scanned document has a lot of room to shrink, because the source resolution is often far higher than needed for on-screen reading. A PDF that started as a Word document or webpage export has very little image data to compress in the first place, so aggressive compression tools often barely shrink it. There's simply not much there to compress.
How this tool compresses a PDF
This tool works by re-rendering each page of your PDF as an image at a resolution and JPEG quality you control, then reassembling those images into a new PDF. This approach is effective specifically because it targets the actual source of bloat in most oversized PDFs, high-resolution embedded images, and lets you directly control the size/quality trade-off with a single slider.
The one thing worth knowing plainly: because this method re-renders pages as images, any text in the original becomes part of that image rather than remaining as selectable, searchable text. For a scanned document (where the "text" was already just an image to begin with), this changes nothing. For a PDF that started with real selectable text, this compression method will make that text non-selectable in the output. Worth keeping in mind if searchability matters more than file size for your specific document.
How to compress a PDF with this tool
- Upload your PDF, the tool reads its page count and prepares to process each page.
- Adjust the quality slider to set the compression level. Lower quality means a smaller file but more visible artifacts if you zoom in.
- Click Compress PDF. Each page is re-rendered at the chosen quality and reassembled into a new document.
- Compare the new file size to the original, then download the result.
Everything runs locally in your browser. Your document isn't uploaded to a server, which matters for anything containing sensitive or private information.
Choosing the right quality setting
For documents you'll only ever view on a screen (reading, emailing, quick reference) a lower quality setting (50-70%) is usually indistinguishable from the original at normal reading zoom, while cutting file size substantially. For documents that might be printed, especially anything with fine print or small text, staying closer to 80-90% quality avoids visible blurriness once ink hits paper.
If the compressed result looks too degraded at your chosen setting, there's no harm in trying again with a higher quality value. Since the tool works from your original uploaded file each time, you're not compounding quality loss the way you would be if you re-compressed an already-compressed file repeatedly.