A lot of contracts still arrive as older Word files. The binary .doc format is what a counterparty exported years ago, or what a system still produces. Asking someone to resave it as .docx before it can be signed is an extra step that has nothing to do with the agreement.
A .doc file can now be uploaded and signed, along with PDF and .docx. You drop the file in as it arrived. The signing flow is the same one used for the newer formats.
The document does not have to be converted by hand into a different Word version first.
