Your attachment contains mergefields and is set up to be used as a mailmerge main document for a letter-type merge with a data source where the fields for each page are all part of the same record (i.e. the same row in an Excel workbook, not on separate rows). The Excel workbook column headings for this would be:
First_Name_Defendant_1 Last_Name_Defendant_1 Address_Line City State ZIP_Code First_Name_Defendant_2 Last_Name_Defendant_2 Address_Line_2 City_2 State_2 ZIP_Code_2 First_Name_Defendant_3 Last_Name_Defendant_3 Address_Line_3 City_3 State_3 ZIP_Code_3
and so on. Using a letter-type merge with that arrangement, the mailmerge would automatically generate a new page for each record.

Your problem description, particularly the part about 'all these extra fields that don't exist in the excel document', suggests you're no longer using the Excel workbook the document was designed for and the new workbook doesn't have the same structure.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]