Compare and Merge Documents

I have an excel document with staff names that I want to merge into
certificates. When I click on compare and merge documents with the word
document (certificate) open, it allows me to select my new document. Excel
is not listed as one of the options for files so I select All Files. When I
try to open my excel document, it goes directly to file conversion.
HELP????? File conversion does not give me any usable data no matter what I
choose.
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pjb
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