Hi,
Create a new object, or use an existing object page and add a code block with the following code: (I have added an image of the item I am referring to on this post).
If Arguments<>"" Then
System.Diagnostics.Process.Start(Application, Arguments)
Else
System.Diagnostics.Process.Start(Application)
End If
For the input parameters, create a data item for both (application & argument - both text) and add those DIs in the "Store In" section of the Start block (see attached for reference as to where I mean).
In your code block, within the same object, set those same DIs to the relevant input parameters - refresh, publish and then save the object.
In your process, or in another object, add the newly created object as an action to your flow and for the input of the new action, set this:
Application: "C:\Program Files\Internet Explorer\iexplore.exe" **or whatever path you have for IE**
Arguments: [Attachment.Value]
When your process/object runs, it should then input the application of Internet Explorer and the URL as the argument to the code stage and it will open IE straight to the URL you wish.
I hope this helps.