Copy the signature of existing POP email that you want to export to a word document.
Open the export wizard by click File -> Open & Export -> Import/Export -> Export to a file -> Choose Outlook data file(.pst) -> Choose you email account, check "Include subfolders" box. -> Next and choose where to save your .pst backup file.
If you are using Microsoft Outlook 2010.
Open the export wizard by clicking File -> Open & Export -> Import/Export -> Import from another program of file -> Select "Outlook data file (.pst) and browse the .pst file that you created in step 3.
Create a new message in Outlook -> Select "Signature" and paste the signature stored in step 2 to "Edit Signature" box.