Attribute creation is an important part in magneto admin panel,
I am going to explain few step by which you can add new product attribute in
your existing product.
1. Go to Catalog->Attribute->Manage
Attributes
2. Let if you want to add datasheet attribute
follow the bellow step showing in pic
3. Again Manage Label Option and set label as
Datasheet as shown in pic
4. Go to Attribute and Mange Attribute set->
Default->
Drag data_sheet from unassigned
attribute to Group
as shown in pic
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