If you see this error
The file could not be converted; it may be corrupt or otherwise invalid (the conversion process failed). Please try opening the file in Microsoft Word, resaving it, and then resubmitting the file for conversion. If this does not resolve the issue, contact your system administrator.
you would never guess what the cause really is. This message does not lead you to the source of failure.
Normally the word automation services work smoothly, but if you are developer and you have a VM with SharePoint, Domain Controller, SQL Server on one machine than it might come to this error above.
The reason for it, was written down in this forum. It seems that the WAS and the domain controller on one machine won’t work.
Try it on a different machine where no Domain Controller is installed. Does it work?