Yes, it is possible to combine two PDFs using Acrobat XI.
Choose 'Create > Combine Files into a Single PDF' and choose the forms that you wish to combine.
Try this and let me know if you face any problem.
Thanks for the response and yes I have tried this but it merges fields with the same name which won't work, so I have tried to create a portfolio which was great but then the document is no longer an editable form.
Therefore, I am still searching for a good solution.