Your standard @INC locations contain /usr/lib64/perl5/vendor_perl/5.26.2, and the file you found, relative to that path, is Image/ExifTool.pm, i.e. Image::ExifTool, and there doesn't seem to be a plain /ExifTool.pm on CPAN anyway. What the script is looking for is a module ExifTool, not Image::ExifTool, and that's part of that repository in the lib subdirectory. Your "workaround" is unfortunately pointing Perl at the wrong ExifTool.pm. Note that when you run perl pdf2john.pl file.pdf, Perl apparently has the correct path in its @INC: "(@INC contains: ./lib ..." - an absolute pathname would be better, but assuming the correct directory layout and current working directory, this should still work. So perhaps you should check that you have the file from the repository in that location?