Hello,
phpdocx is compatible and tested with all versions of MS Word. Maybe when you have created the template with MS Word 2016 it has added some incompatible content with MS Word 2007?
We recommend you to try a template created with MS Word 2007. If you find out the incompatible tag or content created by MS Word 2016 and it's in the body you could remove it using DOCXPath. Otherwise you can remove it manually and package the DOCX again (it's a ZIP file).
Word was unable to open this document. it may be corrupt is a generic error from MS Word when it can't read some relationship or tag or there's a missing Content Type extension.
If you send the DOCX that returns the corruption error to contact[at]phpdocx.com we'll check it.
Regards.