How to use it
Choose a compression preset. Optionally enable Grayscale.
If you need a size limit, enable Target size, enter a number and choose KB, MB or GB.
Run compression and compare the actual result size and page appearance.
Download the results that meet your needs.
Choose the compression strength
A smaller file can involve a quality tradeoff. Compare the result at a readable zoom before keeping it.
Start with Recommended for a general attempt to reduce size.
Choose Strong when a smaller file matters more, then inspect fine text and images carefully.
Try Lossless when you want to avoid the lossy option. The amount saved depends on the original document.
Request a target size
The target is an aim for each file. Some documents cannot reach it without unacceptable changes.
Enable Target size to reveal the size field.
Enter a number and choose the matching unit. For example, 1 MB is different from 1 KB.
Read the measured output size after processing. Do not assume the requested target was achieved.
Decide whether colour is needed
Grayscale converts page colours into shades of gray. This can be unsuitable for charts or documents where colour carries meaning.
Enable Grayscale only if you do not need the original colours.
Inspect a page containing a coloured chart or image after processing.
Disable it and run again if the result loses information you need.
Download and check the result
The result view shows the created output. Downloading a file and checking its contents are separate steps.
Read the output name, count and size in the result view. If processing reported a problem, return to the settings and correct it before continuing.
Choose Download and keep the new file separate from your original. If several outputs are packaged together, open the archive to find them.
Open the downloaded result in a suitable viewer. Check the pages and content affected by this task. Keep your original until you are satisfied.
Output and limits
Target size is an aim per file, not a promise. A small or already optimized PDF may have little room to shrink. Compression can trade image detail for size, so inspect small text and diagrams. It does not split a PDF into pieces to meet the target. Use Split by Size for that.
Compression saves separate PDFs for separate input files. The measured size of the generated file is the relevant result.