Some frequently asked questions about the version numbers in iText.
Why do the version numers jump from 2 to 5, and from 5 to 7? There are several reasons for skipping version numbers. In 2009, the version number of iText (Java) and iTextSharp (C#) were not in sync. The Java version was at version 2.1.7; the C# version was at version 4.1.6. A decision was taken to move to Java 5 for the Java version and to harmonize the version numbers of iText and iTextSharp.
What's the deal with iText 4? Third parties have released iText 4.2.z versions, but those aren't official versions. They aren't supported by anyone and shouldn't be used because no one really knows what's inside.
Is iText 7 backward compatible? iText 7 is a totally new version of iText, written from scratch by the iText team. Backward compatibility is broken in favor of a more intuitive interface. The Java version of iText has moved from Java 5 to Java 7, which was one of the reasons to jump from iText 5 to iText 7.