4DOTS FREE PDF COMPRESS is one of my favorite PDF compressor software for Windows. It has a very simple interface and can bulk compress PDF files with any compression settings. You can generate normal, low, medium, and high quality PDF files using this software.
One of its best features is that you can view the original PDF size and compressed PDF size directly on its interface. Thus, you can easily check how much size is reduced for every single PDF file. Add PDF files, set the compression option, and begin the compression process.