Alfresco has format conversion (or better transformation as it is named in Alfresco) build in. A lot of formats are supported out of the box. The document transformation can be done form a rule or script, triggered by events like "document updated" or "document created". It is also possible to add custom transformations. The mimetypes webscript provides a list of possible transformations.
In Alfresco Share there is currently no user interface for document transformations - however I know that this module implements a transformation dialog http://www.ecm-market.de/xkey-autoocr-transformer.html where you can choose various target document formats.
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