Start with the least destructive pass
Some PDFs shrink cleanly by removing unused structure or recompressing embedded images. Others are already optimized and cannot reach a tiny size without rasterizing pages or lowering image quality.
If the document contains selectable text, links, forms, or signatures, check the result before relying on it. Compression should not silently pretend that every PDF can be reduced without consequences.
Watch limits on large documents
Browser-local processing uses the memory and CPU available on the device in front of you. A desktop can usually handle more than a phone, while a very large PDF may take longer or fail if the browser runs out of memory.
For private files, that local cost is the point: the document stays in the browser instead of being uploaded to a remote compression service.
Verify the output before sending it
Open the compressed file and inspect the pages that matter most: signatures, tables, fine print, scanned pages, and anything with small text.
Also check the final file size directly. A target such as 200 KB or 300 KB is useful, but not every source document can reach it while staying readable.