Open a new TI-Nspire document on your PC. Instead of "converting" the PDF file, you use the "Insert Image" tool.
Here is a blog post detailing the top free options and how to use them. pdf to tns converter free top
The TI-Nspire is a powerful tool, but its operating system is designed for math exploration, not general document viewing. Converting your PDFs to TNS allows you to: Open a new TI-Nspire document on your PC