I have a very large ebooks; I would like to reduce their sizes while maintaining the highest possible quality.
Is there a best PDF compressor software or online website that I can upload my private ebooks to?
Note: I'm looking for a safe website that won't share my ebooks.
I'm not sure what you mean by best. Best is subjective and dependent on various factors such as type of PDF document and acceptability of quality loss.
However, Adobe Acrobat Pro DC offers an option to Reduce File Size.
Similar software also offer such an option. Example: ABBYY FineReader (p. 3 of Source).
Use Ghostscript, it's the best software for your task. You save your ebook locally, and nobody can share your ebooks.
It's available for Linux and Windows, and has many usage examples.
