PDF compression is the method of reducing the size of a PDF file. Compressing a large PDF file before sending it via email or uploading it to a website can be useful. There are several online apps that can help you compress PDFs. ToolsZuTools is one such application. It is a free online PDF compressor that allows you to compress a PDF document without installing any software. Select your PDF files for compression by clicking the "Choose Files" button. Click the "Compress PDF" button to begin the compression process. When the status changes to "Done," click the "Download PDF" button. It's a free online PDF compressor that lets you compress any PDF file right in your browser.