Why would you need to compress PDFs? Since PDFs can get pretty heavy in size, you might face limitations with sharing them. For example, if you have a PDF that’s larger than 50MB, you might not be able to upload it to certain websites. You might even have trouble emailing it, depending on which email service you use. Compression is a way to make an existing PDF smaller. With PDF compression, you can optimize your document(s) so they are easier to share and take up less space on your hard drive