There is only one file type that uses the .PCAST extension:
iTunes Podcast File
XML file created by iTunes, a music shopping and playback program; contains information for subscribing to a podcast, including the link, title, category, and subtitle; used for sharing recommended podcasts or favorites with others over email or the Web.
PCAST files can be created by selecting an iTunes podcast and dragging it to the desktop. After receiving a PCAST file, you can double-click it to automatically subscribe to the podcast. iTunes will then automatically begin downloading the latest audio files.
NOTE: Since PCAST files are stored using XML formatting, you can view them with any text editor.
Updated: June 27, 2015