When a workflow runs for a document in the document library, it might be necessary, to insert a hyperlink to the document into the form. To achieve this, the following steps are needed, all in one process container:

First build the URL and store it in the field of the process. Use a Data event:

Now copy the content of this process field into a field of the InfoPath form:

In the InfoPath form simply insert a hyperlink:

And the result: