SlimPDF

SlimPDF is a lightweight PDF reader that occupies up to 20 times less space on the hard drive than some of its competitors, like Adobe Reader and Nitro Reader.

The application lets you open multiple PDF documents simultaneously and keep them in different windows. However, there's no sidebar for quick access to pages and chapters like the ones included in other applications like Adobe Reader.

Of course, the SlimPDF interface is attractive precisely because of its simplicity. There are only a few buttons on the toolbar for the most basic and essential commands like turning the page or adjusting the page width to the screen.

SlimPDF is a great option for less powerful computers or ones with limited space on the hard drive. Although it doesn't manage large documents very well, its overall performance is pretty good.