The iText website has two main areas:
itextpdf.com: This is the part of the site aimed at customers, where they can find information about the different products and partners, and can explore use cases and pricing packages.
developers.itextpdf.com: This is the part of the site aimed at developers, where they can find references (e.g. API), tutorials, downloads, etc.
Visitors can switch between the two areas by clicking the right-most button in the menu bar saying customers and developers respectively.
The menu bar of the customers area:
The menu bar of the developers area: