Get link address of a file I have a page A that has an inline entity form that is referencing to page B, it's possible programmatically or in another way to get the link address of a file that page A is referencing to?
Yes it is possible, but that's a quite broad question. And it depends a little bit what exactly want to achieve and where.

Basically when you have the node object of page B you also have the field value of the reference field, which will be a node ID. The node ID of page A. You can take this node ID to load node A – node_load($nid).

Then you have the node object of node A. And from there you'll get the field value of the file field which most likely is a file ID. This file ID now can be taken to build the path to the file – file_load($fid).