wpsx to docx conversion is most likely searched by users that own old documents from WPS Writer, later known as Kingsoft Writer and would like to convert these files to MS Word or at least open them.
Most tools actually discontinued support for Kingsoft's formats and it is pretty difficult to even open these files nowadays, unless you have access to the original software. Your best option, and perhaps even only one, is to actually look for installation packages of old Kingsoft Office and use the word processor app to export your documents to RTF or something like that, which can be then opened/imported in Microsoft Word.
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