Can An Application Process Documents That Use Xml Namespaces And Documents That Don’t Use Xml Namespaces?

Yes.
This is a common situation for generic applications, such as editors, browsers, and parsers, that are not wired to understand a particular XML language. Such applications simply treat all element type and attribute names as qualified names. Those names that are not mapped to an XML namespace — that is, unprefixed element type names in the absence of a default XML namespace and unprefixed attribute names — are simply processed as one-part names, such as by using a null XML namespace name