You will also get that error if there is an error in the code that makes it incompatible with Word 2016. As you have not shared the code it is not possible to form a judgement about what is causing the error. One possibility is that you have installed the 64 bit of Office 64 and the code is not compatible with that version.

As the add-in is concerned with find and replace, you could try instead http://www.gmayor.com/document_batch_processes.htm which includes find and replace options and which is compatible with Word 2016 and should be with the 64 bit version.

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Graham Mayor - MS MVP (Word) (2002-2019)
Visit my web site for more programming tips and ready made processes www.gmayor.com