1.  Try running the report again if possible.

2.  If that is not an option, open the file with a text editor.  If the first line of the file looks something like:
 
%!PS-Adobe-3.0
%%Creator: Oracle Toolkit 2 for Motif 6.0.8.22.0 PRODUCTION
%%Version: 6.0 8

then the file is in Postscript format.  To convert the file to PDF format, use a utility, such as on https://online2pdf.com/convert-ps-to-pdf.