I’ve done some work with the iTextSharp libraries directly in PowerShell before. You can see an example at Search a PDF and return specific text . You will need to download a copy of iTextSharp.dll.
That function was written specifically for the question posted on that thread, looking for section numbers followed by some number of lines matching ABC-*. It’s not meant for you to be able to run it directly.
However, the code does show you how to use the PdfReader and PdfTextExtractor classes to pull text out of a PDF into a .NET String variable. From there, you can split it by line as in the example, or just work with the whole page text as one string; that’s up to you.
Here’s a more trimmed down example that just extracts all of the text from the PDF and outputs it as a single string, that you can manipulate however you want: