Imported PDF files are not automatically transformed into the Song One format. Once a PDF file is added you may create a native Song One file if necessary. While both the native Song One files and PDF files can be used in the same song catalog they differ in the features they offer:
To import a PDF file click/tap on the inward pointing arrow in the upper left corner of the library panel. (If the library panel is not visible tap/click on the three lines in the upper left corner of Song One's main window.)
Once a PDF file has been added to the song catalog it will open in Song One's main window. A PDF icon in the bottom toolbar indicates the document's format. A black lock in the upper right corner of the screen informs you that the document cannot be edited except for annotations.