I see the problem you are having, but I'm not getting through to you.
I would suggest you get a copy of my book https://www.amazon.com/Microsoft-Office-Access-2007-VBA/dp/0789737310/ref=cm\_cr\_arp\_d\_product\_top?ie=UTF8
Don't worry about the 2007, VBA hasn't changed appreciably since 2007. What you really need to understand is how variable work. I'll give you a brief summary.
A variable is a name you apply to a value being used within your code. Variables are usually defined using a Dim statement. Once a variable is defined, it can then be assigned a value. However, if a variable is created and no value is assigned, the variable contains a Null value.
Access is an object oriented p0latfomr. Everything is an object that has properties, one of which is the Name property. So, Controls on a form need to have names that you can reference as well as variables need to have names.
So in your code you DIM only strFile, but you never assigned a value to strFile. So when you try to open strFile vial FollowHyperlink there is nothing to open.
I'm also unsure why you are choosing the DblClick event instead of just the Click event. One usually usualy Click for a command button.
You refer to controls on your form via Me.DigitFileName1 and Me.DigitFileName2. Do you have 2 controls on your form with those names?