What app or program are you using to remotely access the My Cloud? The WD Desktop program? The MyCloud.com user web portal?
Using the WD My Cloud Desktop program on Windows (http://setup.wd2go.com/index.php?mod=download&device=mc) I can remotely open, edit, and save Excel and Word files from a remote My Cloud.
Unofficially, and absolutely not supported by WD, if one has a first gen v4.x My Cloud they can install the unofficial CloudDAVMod which will allow one to remotely map the My Cloud so they could remotely open/edit/save to their v4.x My Cloud.
https://community.wd.com/t/app-clouddavmod-various-versions-for-firmware-v4-09-2016/161543
