i have this line in my Web.Config
<add key="localhost2" value="http:\\export\" />
in vb Code:
<a href='" & ConfigurationSettings.AppSettings("localhost2") & TransactionNo & "\" & fi.Name & "' target='_blank' >" & fi.Name & "</a>"
the Publish URL :
How i can encrypt the 803 value or prevent the user from change the value in address bar?

I think your best bet is to add uthentication to each directory that user might use. This way even if they change the url they won't be authorized to enter that directory.

Max security is authentication at the resulting url or at least use the same function that provides available transaction numbers for that user;

Medium security would be to use an obfuscated value such as a GUID rather than a transaction number. This would probably mean adding another field to your db.

A more cumbersome solution would be to render the detail inline - returning your complete dataset - which would mean that the url would never change.

i added authentication make user just to read from the directory , but still can open the file