If you attempt to open a MISMO XML file, you will either see a blank screen or what appears to be gibberish, depending on which program on your computer attempts to open the file.
A 1004 report in MISMO XML format, opened in Internet Explorer.
This is normal. MISMO XML files are not meant for human use or understanding; they are a computer-readable version of your report. This is one reason the MISMO XML creation process gives you both the XML file and a PDF: you and your client can refer to the PDF file, and your client can forward the XML to FNMA.