Puting a Link to ext File or directory to a cust-Field through Membrsh/contrib A

[Markus Hapke]

Hello all of you

We want to add some files to the membership or contribution. These files we put in a new directoy orgnized by Civi-ID numbers.

Now these files should be reached quick from out of the contact or membrshp or contrib.
This should be realized via a new custom field (type Link) which shall carry a
link to that directory. This field should be filled with a API - Call of the respective entity (update/create).

But whenever we put the path-info  in that field it cannot be selected correct. 
Any advices for this?   Our code coming soon.

best regards, M.Hapke