This extension handler extends the third-party installed PDF filter handler (the shell extension used to extract text and metadata properties from the PDF files, e.g. used by the Windows Search to index the PDFs text content) in order to make the filter to also extract any of the custom defined properties data. This extension is useful to enable access to custom fields metadata by tools that are not able to use the property handler and rely only on filter handlers. PDF filter handlers don't usually export metadata properties, only text content, or only support the standard PDF properties.