If you decide to link a document from a document library using some of the built in SharePoint links web parts, you will encounter a strange behavior of Office clients. Your document will be opened as read-only and you will not be able to save it.
There is an KB article which describes how you could modify registry in order to avoid that.
However, I prefer my own simple solution. In order to use it, you will need to know a little bit of HTML and that’s it.
Instead of links web part you should use Content Editor Web Part and create a link like this one:
<A HREF=”[%DOCUMENT_URL_HERE%]” onclick=”return DispEx(this,event,’TRUE’,’FALSE’,’FALSE’,’SharePoint.OpenDocuments.3′,’0′, ‘SharePoint.OpenDocuments’,”,”,”,’30’,’0′,’0′,’0x7fffffffffffffff’)”>Document name here</a>
The key difference here is the DispEx function which will be called when someone clicks this link. The document will be opened in the appropriate Office client application and you will be able to edit it.