In the first step should define the files.In this example are the files in the same directory how the test class
File example1 = new File( getClass().getResource( "Example1.pdf" ).getFile() );
File example2 = new File( getClass().getResource( "Example2.pdf" ).getFile() );
after them initial the comparer and compare two pdf files
ResultModel result = pdfComparer.compare( example1, example2 );
and now use the standard JUnit methods
Assert.assertEquals( <expected difference>, result.getDifferencesCount( false ) );