I have used iText in the past...so I'm not completely green. However after installing the NuGet iText 7 dot net package, I can't seem to figure out the references to iText7. Is it not just : using iText.text.pdf.parser; using iText.text.pdf;
And so on?
The text extraction API is pretty much the same in iText 7 as in iText 5, only in iText 7 there are a number of bugs that have been fixed over the last year, and work is underway to improve the tooling. The namespace of the text extraction API in iText 7 is iText.Kernel.Pdf.Canvas.Parser.
There isn't a direct mapping for most classes and use cases, because most functionality has simply been reimplemented with a different way of working. Rather than doing old things with new tools, we prefer that users understand the new tooling and start doing new things with it. In the core functionality, only the text extraction and digital signatures APIs are very similar to iText 5, and for all the rest we recommend looking at the tutorials, most prominently the Building Blocks and the Jump-Start tutorial.
For the record: I am an iText Software employee.