I suppose that small pdf was one of first sites to process PDF documents. In last months there were tons of similar sites. More or less all of them have similar option but main difference are limits. For example, small pdf allows only 2 documents to be processed per hour for free or you need to have subscription. On the other side PDFtodo (https://www.pdftodo.com) allows you to process up to 10 documents at once and you can repeat process unlimited number of times. Of course, PDFtodo is free and that is clear advantage compared to other similar sites. PDFtodo has 23 different modules to compress PDF, split PDF, convert Images to PDF or to convert PDF to Images, and more...