Your question is extremely vague. We will need for you to provide more detail.
From the context, I am guessing you may be talking about Acrobat ("Adobe" is the company, not the name of the program). Are you trying to combine files in Acrobat?
Please let us know what version of the program you are using (Acrobat Pro? Standard? Version X? XI? DC?), what operating system and version you have (Windows? Mac OS? Version?), and what process you are using to combine the files - and what errors or results you are getting. We can only help if you provide more detail.