This was created for the Mac OS X operating system. Unlike the old operating environment versions, the font is stored in the thread of a data file instead of in resource threads. It’s been used as a container for TrueType fonts since 2009 after the release of Mac OS X 10.6, and is gradually replacing the TrueType Collection.
This format is used to store templates and designs in PageMaker 3. PT3 allows for a set of font descriptions, and for the layout and graphical elements to be stored in PostScript Type 3 format. This container is used as an editable file to meet publishing needs, and was created in a program for the PageMaker layout.