This week's book giveaway is in the Programmer Certification forum. We're giving away four copies of OCP Oracle Certified Professional Java SE 11 Programmer I Study Guide: Exam 1Z0-815 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
I'm just curious. Are you using Spring ? If so, you should not use the response to write anything to it. The iText document will be output to the response automatically by Spring (which causes an IllegalStateException). Just write to the document. The response should only be used to set cookies or http headers.