When you develop an application reading or writing PDF files, it may be useful to inspect the content of a file in order to understand what is inside and how objects are linked. Especially when dealing with PDF version 1.5 or above when multiple objects can be compressed together into an object stream: opening the raw file in a text editor would not help you. You can find similar tools with a text based interface or with a Java client, but I am not aware of another tool producing HTML for easy navigation in the PDF structure.