How to open .pdn files? or: Things I wish I'd known earlier.
Paint.net is a graphics program uses its own binary file format .pdn that almost no other program can open. Paint.net has a large community and many plugins are available including a third part plugin that adds support for OpenRaster. Paint.net is written in C# and requires the Microsoft .Net runtime, meaning current versions work only on Windows Vista or later.If you need to open PDN files without using Paint.net there is an answer! Lazpaint can open .pdn files and also natively supports OpenRaster.
In hindsight using Lazpaint would have been easier than taking a flat image and editing it to recreate the layer information I wanted. Although I respect the work done by Paint.net it is yet another example of time wasted and hassle caused by proprietary file formats and vendor lock-in.