Solvusoft explains that a PRN file or file with a ".prn" extension includes the contents of a document to be printed and instructions for the printer. If one opens it with a Windows editor, an encrypted page typically appears. Instead, one can use notepad.
The fastest and the easiest way to open a PRN file is to double click on it and wait until the operating system or OS automatically selects which application to use to open the document; the OS often selects the incorrect one. Check for the file registry settings on Windows, and select an application such as notepad to see what is inside a PRN file and the cause of the encryption. A PRN can be associated with a DataCAD Windows Printer File, Printer Text File or other printer software programs.