If it appears as an icon in the body, then single-click the icon so that a single-line border appears around it. Once you have that, you should be able to drag it into the Contacts folder. If you do other than single-click it, you may see that the border around the icon has eight blocks in it; you will not be able to drag the contact at this point.
If the contact appears in the header section, single-click the contact in the header and then drag it into your Contacts folder. If it does not drag, wait a moment, click it one more time, and then try the drag operation again.
If none of the above work, you can open the contact and then select File -> Copy to Folder to put it into the Contacts folder.
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This was first published in January 2007