At first glance, many documents are apparently identical, but in the majority of cases they differ somehow; for this, it is useful to have a tool like Compare Suite, which lets you compare distinct documents, looking for any difference, however small.
Compare Suite lets you compare documents in MS Word, Excel, PDF, HTML, TXT, DOCX, XLSX, and even Open Office. It not only lets you compare among these offic formats, but also among files compressed with ZIP or RAR.
When doing the comparison, Compare Suite shows the exact point in the document of the difference.