If you are speaking of data files processed by a program as it runs, then reading values from a record of a file is either under format control (a FORMAT statement or format string contained as a literal within the READ statement), or the READ statement specifies no format (just "*") and the data values on the record are separated by blanks or commas (and multiple records could be absorbed to satisfy the whole READ list. This is a bit simplified; consult a good Fortran manual.
Now if you are speaking of the format of Fortran source files, as your last sentence suggests, you can have one file be in fixed format (statement numbers in columns 1-5, continuation character in column 6, statement body in columns 7-72), and another file be in free format (no column designations, lines to 132 characters, different designation of continuation lines), and compile each file separately, telling the compiler which form to expect for each. Your compiler may have a command line or default switch telling it which form is given, or it may take the form from the file extension; the Lahey LF95 compiler offers both ways. But you can't combine files so that one part of the file has a subroutine in fixed format and another has a subroutine in free format. Refer to your Fortran language manual for rules on the different forms.
