At www.docx2doc.com we keep track and monitor our conversion success rates. Note that we do not store any files on our server, but we keep statistics on whether files convert properly so we can improve our service.
We found out that we can increase the success rate of converting documents by adding multiple conversion algorithms. If one method does not work we automatically try to convert your docx files to doc using a secondary method.
Our overall success rate for converting docx documents was very high to begin with, but we felt adding an alternate method in the rare case the first one failed would only be a benefit. All of the document conversion is done real time on the fly so you won't see what is happening and just get your converted file back automatically.
We hope you enjoy the reliability of our docx to doc service and do our best to improve it as much as possible.