Attach database in MS SQL Server Management Studio did not work

I successfully installed MS SQL Server Management Studio on my computer (windows10). 
I connect to the server name: SQLEXPRESS, Authentication: Windows Authentication.
I would like to attach the Northwind database which I have downloaded from here: https://www.microsoft.com/en-gb/download/details.aspx?id=23654 and installed on to my C: drive: C:\SQL Server 2000 Sample Databases\NORTHWND.MDF
I have edited the permissions of the database to allow full access.
However, when I try to attach from the management studio I get the error message below.
Can you tell me why, perhaps I've missed something, and how to resolve it please?
Kind regards, SB

Error message:
TITLE: Microsoft SQL Server Management Studio
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Attach database failed for Server '\SQLEXPRESS'.  (Microsoft.SqlServer.Smo)

For help, click: https://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&ProdVer=15.0.18206.0+((SSMS_Rel).191029-2112)&EvtSrc=Microsoft.SqlServer.Management.Smo.ExceptionTemplates.FailedOperationExceptionText&EvtID=Attach+database+Server&LinkId=20476

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ADDITIONAL INFORMATION:

An exception occurred while executing a Transact-SQL statement or batch. (Microsoft.SqlServer.ConnectionInfo)

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Unable to open the physical file "C:\SQL Server 2000 Sample Databases\northwnd.ldf". Operating system error 5: "5(Access is denied.)".
CREATE DATABASE failed. Some file names listed could not be created. Check related errors. (Microsoft SQL Server, Error: 5120)

For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft%20SQL%20Server&ProdVer=14.00.1000&EvtSrc=MSSQLServer&EvtID=5120&LinkId=20476

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BUTTONS:

OK
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