This User Manual icon is made in Material Design style developed by Google. This style is based on extremely simplified shapes, thin two-pixel lines, and is optimized for 24x24 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 4,400 icons, all in the same style and quality.
This icon for User Manual looks like an open book. The cover of the book looks like a rectangle with rounded edges, and two pages are visible, separated by a line in the middle of the pages. On the page on the right, there is a large lower case letter i.