When exporting an Epic with a custom layout definition to either PNG or PDF format, the custom layout definition is not used. Instead, the default layout is used with the the Overview tab over in the right panel. Since the right panel is a narrow column all the content in the Overview section (that includes Use Cases, Functional Requirements, etc.) is crammed into a very long column with the rest of the page left blank.
So, whether sharing as a file or as part of a presentation, this makes for a highly awkward format and presentation of the information. Recommend that the export use the Custom Layout as a basis to avoid this problem and make for a far more acceptable and user friendly output.