The content export/rendering pipelines (versioned and not versioned) in the CMS workspace can't handle binary formats:

<map:match pattern="_content.*">
    <map:act type="get-content">
        <map:parameter name="id" value="{request-param:contentId}"/>
        <map:parameter name="contentVersion" value="{request-param:contentVersion}"/>
        
        <map:generate src="cocoon://_plugins/{plugin}/{contentType}.{../1}"/>
        <map:serialize type="xml"/>
    </map:act>
</map:match>

If "_content.pdf" is called to generate a PDF version of the content, this pipeline is still serialized in XML...
The pipeline should be reverted to a "map:redirect-to" instead of generate/serialize calls.
This bug applies to the versioned "_content/v_**.*" pipeline as well.