is there a way to append the attached pages to the document in forms
There are 2 ways you can go about this. Probably the easiest way is to use Workflow. Once the form is saved to the repository, in Forms you could have another task in your business process that starts a workflow to join the 2 documents together using the instance id and/or bpid as a search key. The second option is a little more complex. It would require some javascript. It is more of a workaround and I'm sure not suggested or supported by Laserfiche. Let me know if you need more details on the implementation.
the problem is forms attachment when saved to repository does not generate pages , so in that case you can not use workflow to mergethe pages because there will be no pages in the attached document.