These _PDF files are generated by Microsoft Live Mail. This software sometimes changes the extension of PDF files from the standard .pdf extension to _pdf.This usually happens when the PDF file has a dot (.) at the end of the file name and another dot for the extension. Because a dot should separate the file name from the extension, some programs like Windows Live Mail may change the dot of the extension to an underscore in instances where there are two dots before the extension.Other users claim that Microsoft Live Mail and newer versions of Internet Explorer may sometimes do this upon transmitting PDF documents to and from the Internet, even if there is only one dot before the extension. To open _PDF files, simply rename the PDF document to a standard .pdf file. This means you must delete the underscore () and ensure that there is only one dot before the PDF extension.
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