HP Fortran Programmer's Guide (B3908-90031; September 2011)

Using Fortran directives
Chapter 9206
Fortran directives.
HP Fortran also recognizes C Preprocessor (cpp) directives. If you compile with the +cpp=yes option or if
the name of the source ends in the .F extension, the source files are first passed to the C preprocessor for
processing. For information about the C preprocessor, refer to cpp(1).