Compress PDF File
Reduce the file size of your PDF. Note: Basic compression is available. For best results, consider using specialized compression tools.
Compress PDF Files Online - Free Tool
PDF compression reduces file size primarily by downsampling embedded images and re-encoding them at a lower quality. Text, fonts, and document structure are not affected. This tool runs server-side - your file is sent over an encrypted connection, processed in memory, and deleted immediately after the result is returned. It is never written to disk.
What the Three Compression Levels Do
Each preset controls how aggressively images are downsampled and re-encoded. Text is not affected by any preset.
| Low | Medium | High | |
|---|---|---|---|
| Image downsampling | None | 150 DPI bicubic | 96 DPI bicubic |
| Monochrome downsampling | None | 150 DPI | 120 DPI |
| JPEG quality | 80 | 70 | 52 |
| Best for | Print-ready files, portfolios | Reports, email sharing | Maximum size reduction |
After processing, the tool compares all candidate outputs and returns whichever is smallest. If a PDF is already well-optimized, the original file may be returned unchanged. If you want to learn more about how compression levels affect visual quality and when to use each preset, our blog article on PDF compression and quality covers the key differences in plain language.
When Compression Works and When It Does Not
The amount of size reduction depends on what the PDF contains:
- Image-heavy PDFs see the largest reductions, especially on Medium and High presets, because image downsampling and JPEG re-encoding remove significant data.
- Scanned documents are effectively image-only PDFs and compress well at higher presets, though text sharpness decreases at 96 DPI.
- Text-only PDFs see little benefit because there are no images to downsample.
- Already-optimized PDFs may see no size reduction at all. The tool will return the original in that case.
If your file remains too large after compression, use the split tool to divide it into smaller sections, or the optimize tool which runs the same pipeline with additional structure cleanup options.
How to Compress a PDF
- Upload your file: Click the upload area or drag and drop your PDF. The file is sent to the server over an encrypted connection for processing.
- Choose a compression level: Select Low, Medium, or High depending on whether you need to preserve image quality or minimize file size.
- Remove metadata (optional): Check "Remove document metadata" to strip author, title, creator, producer, and other fields from the output file.
- Download the result: The server returns the smallest output it could produce. The original file is deleted from server memory immediately after the response is sent.
Watch How It Works
See the tool in action with this quick tutorial video:
FAQ
PDF compression works primarily by downsampling embedded images to a lower resolution and re-encoding them at a reduced JPEG quality. Text and fonts are stored as vector data and are not affected. The tool also removes structural overhead such as unused objects and redundant data from the file. It compares all output candidates and returns the smallest one. If the original is already smaller than any processed version, the original is returned unchanged.
Low compression applies JPEG re-encoding at quality 80 without downsampling images. Medium downsamples color and grayscale images to 150 DPI and applies JPEG quality 70. High downsamples color and grayscale images to 96 DPI and monochrome images to 120 DPI, with JPEG quality 52. Higher compression produces smaller files but reduces image sharpness. Text is not affected by any of the three presets.
If a PDF was already compressed or optimized before uploading, the tool cannot reduce it further. Text-only PDFs also see minimal reduction because there are no images to downsample. The tool returns the original if it is already the smallest candidate. Trying a higher compression preset may produce a smaller result, at the cost of image quality.
No. Text in a PDF is stored as vector outlines or font data, not as pixels, so it is not affected by image downsampling. Only raster images are re-encoded. On scanned documents, where pages are stored as images rather than text, higher presets will reduce the sharpness of text because it is part of the page image.
Yes. The tool includes a Remove document metadata option that strips the author, title, creator, producer, and other fields stored in the PDF info dictionary and XMP stream. Check the option before compressing. The metadata is removed from the final output file after compression completes.
No. The file is processed entirely in server RAM and deleted immediately after the compressed result is returned to your browser. It is never written to disk, stored in a database, or retained after the request completes.
Image-heavy PDFs see the largest reductions, especially presentations, brochures, and documents exported from design tools. Scanned documents are also good candidates because every page is a raster image. Text-only PDFs such as contracts and reports generated from word processors see minimal reduction. PDFs that were already exported with aggressive compression settings before uploading may see no reduction at all.
Compressing the PDF itself is usually better. A ZIP archive wraps the file without reducing its internal size - the recipient must extract it before opening, and many email clients and portals do not accept ZIP attachments. PDF compression reduces the actual file size so it opens directly in any PDF viewer without an extraction step. ZIP offers negligible additional size benefit on a PDF that is already internally compressed.
Both tools use the same compression pipeline. The optimize tool additionally linearizes the file for fast web viewing, which restructures the PDF so that the first page loads before the rest of the file is downloaded. For most size-reduction tasks, either tool produces the same result.
Yes. Scanned PDFs store each page as a raster image, which makes them good candidates for compression. The High preset downsamples page images to 96 DPI and re-encodes them at JPEG quality 52, which significantly reduces size. The tradeoff is that text on the scanned pages becomes less sharp because it is part of the image. If you need to extract text from a scanned PDF before compressing, use the OCR tool first.
Try the High preset if you have not already, which applies the most aggressive image downsampling. If the file is still too large, use the split tool to divide it into smaller parts and share them separately. For documents with many embedded images, extracting and removing unnecessary images before recompressing can also reduce size significantly.