S Agarwal wrote:1) How iText is dealing with different versions of PDF available in the market?
All versions are supported, but for very specific reasons, the default version is 1.4 (among others because some ISO standards such as PDF/A and PDF/X are subsets of PDF 1.4). In some cases, iText will change the version to a higher number automatically (for instance if you use functionality that was introduced after PDF 1.4).
S Agarwal wrote:2) Can iText read/parse all versions of PDF available in the market?
All versions that are described in ISO-32000-1 are supported by iText, but be aware that there are tools that create broken PDFs. In some cases, iText can read those broken PDFs, but in general you shouldn't use tools that don't respect the ISO standard.
S Agarwal wrote:3) Is security handled in iText?
This has already been answered in another topic:
https://coderanch.com/t/515934/open-source/iText-security
S Agarwal wrote:4) Is there any .Net version of iText available?
Yes, there's a C# port named iTextSharp.