Word 2010 is not supported by RoboHelp 8, that is the cause of the problem. You need to revert to an earlier version. You can have both on your PC at the same time subject to valid licences.
To create a PDF of anything, you have to create a file with other software, Word, Excel, etc. What RoboHelp does is create a Word document behind the scenes, create the PDF and then trash the temporary document. No valid version of Word so it cannot do that.
See www.grainge.org for RoboHelp and Authoring tips
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I'd be surprised if Adobe issued a patch to make RoboHelp 8 work with Word 2010. The next version will likely bring that compatibility.
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