Phoxgrimm9 ... You will need Pepakura Viewer v.3 to open WebDude's .pdo files. I don't think v.3 is still offered on the Pepakura site, but it is still available to download from here ...
Pepakura Viewer 3.0 Download (Free) - pepakura_viewer3.exe
Once you get the PDO open in Pep Viewer you should be able to print to PDF if so required.