Free Online PDF Compressor

This usually means your document contains very high-resolution photographs or was scanned at an extremely high DPI. Try the deeper compression mode, which engages more aggressive image downsampling and internal garbage collection. Most email clients cap attachments at 20 MB or 25 MB — our PDF optimizer online can bring the vast majority of documents well under that threshold. If the file is still too large, consider splitting it into sections first.

Scanned pages are essentially images saved page by page inside a PDF container. To compress them without making text unreadable, use the deeper optimization mode, which targets the image DPI for each page intelligently. The goal is to lower resolution just enough to slash the file size while keeping the text recognizable. For documents scanned at 300 DPI or higher, you can usually reduce PDF size substantially and still keep the content perfectly usable.

Select the deepest compression setting available in the tool. This mode applies aggressive image downsampling and removes all unnecessary internal data, which can bring even large image-heavy documents down to 500 KB or below. If your document is a text-only PDF, the savings will be smaller since there is little image data to remove. For scanned academic submissions, Deep mode almost always delivers the target size.

You can try, but results will be limited. A PDF that has already been optimized has had most of its redundant data removed. Running it through a compressor again will find very little left to shrink, and you risk marginal quality loss with minimal size benefit. If your file is still too large after a first pass, the best approach is to use a higher compression mode, reduce the number of pages, or remove high-resolution images before re-exporting from the original application.

Not directly. The tool needs access to the document's internal structure to optimize it, and encryption blocks that access. You will need to remove the password locally first — most PDF readers let you do this if you know the password — then upload the unlocked file for compression. Once you have the optimized output, you can reapply password protection using your preferred PDF editor.