Edit a PDF using flpsed

I've been looking for a simple tool to annotate PDF files.   Since going paperless, I've often wanted to annotate scanned images with additional information.  Well, I finally found a tool that is light weight and simple to use.  It is flpsed.  Some advice on its use:

1. When using "Save As", ensure this is saved with file extension ".ps" so not to get confused.  
2. "Export" the finished annotated document as a PDF.

To Do: How to use an external tags file?  I assume this is a PostScript file containing key/value pairs.