Comments by KimberleeL (Top 3 by date)

Hi Madhulika, you can use some library that can convert those external CSS into an inline CSS before you use iTextSharp on that HTML content.
For example check the following StackOverflow post:
.NET convert external CSS to inline CSS[^]
But unfortunately iTextSharp has some difficulties with processing HTML content, so instead I used this approach:
Convert HTML to PDF in C# and VB.NET[^]

You shouldn't post question as an answer to a previous question, it can easily be overlooked.
Now regarding your issue it depends on what iTextSharp version you are using, but nevertheless I had a similar issue and this SO discussion the required information for resolving it.
In short notice the use of IMG_BASURL and also the use of IMG_PROVIDER in the one of the below posts.

Also just in case you are interested there is an alternative approach that you can use in order to create a PDF file in C#.
Check out the following article that shows how to convert a HTML content into a PDF file in C# with a use of this .NET library for Word processing.