Add field linking to related node
You can do this in two ways.

Option 1:
Add a textarea field to the file content type, with the necessary text options (fe html on etc), and create two various displays via Display Suite. Create a view block with the nid as contextual filter. 
And select the node display for showing.

Option 2:
Install the prepopulate module and setup a rule that after saving the html content type node redirects to file content type with the right url + prepopulate information. Have 2 separate content types. In the file content type add a reference field with prepopulate settings.

Now after you create the node with html information it redirects to the file content form with the reference field filled... So no searching and no hassle.