Bruno Lowagie's Online Gazette

James Gosling said it about JDK 1.4 users: Will You Please Stop Using 1.4.2... There was a Death to IE6 website. At iText, we strongly discourage the use of versions prior to iText(Sharp) 5 for both technical as well as legal reasons.

TECHNICAL REASONS: the MPL/LGPL version of iText(Sharp) dates from July 2009. Many bugs have been solved in the meantime. For instance: we fixed a bug that was hard to reproduce, and that made a row in a table disappear if specific conditions were met. These conditions occurred in only a very small fraction of the total number of rows added to tables. Also: the spec has evolved. For instance: digital signatures in the pre-5 versions of iText are either forbidden (in the PAdES standard) or will be deprecated (in ISO-32000-2). Suppose you still use those old signatures, then you automatically exclude yourself from extending the life of the signed document for instance by using LTV (PAdES part 4).

LEGAL REASONS (copy/paste from our attorney): Older versions of iText under the free model may contain code fragments that infringe other peoples copyrights or intellectual property rights. iText Software Group has done a significant investment in identifying and eliminating all those case as of version 5.1. which is one of the reason why it is now a paying commercial version. We do not recommend the use of versions prior to 5.1 for commercial projects as your company could be liable for copyright or IP infringements.

Personal note:
My name is Lowagie, and every time you type import com.lowagie, you're using MY name.
Please respect my name, and follow my advise: upgrade to the latest iText version.

Update:
See also When I Realized I Used A Library That Was Deprecated.