Write to a "writable" PDF file in .net

Question

This question might have been answered already and I looked into the web, but I don't really know what term to use, but here it is.

As some of you know, some people provide writable pdf file, basically look like some web form, but in pdf format, in which there are fields that can be filled. One of our client have such a form and would like to be able to fill in the fields from a software that we wrote. Most of the fields are there and we can easily add the one missing, but we have two main problems with this

• I can't find a way to actually write to those documents.

• The document is provided by a government entity, which seems to update it with new change several times a year. Plus they only accept the most recent version.

My question is : Is this even possible and if so how do we do that ? When I look in the web, I find all ressource on how to write a PDF in c# or other language, but how to write in to those PDF form.

Thanks,