Merge PDF files in Acrobat Reader?

++ adding on further information

For more details on how exactly it works, you can refer to the help article here: Combine or merge files into a single PDF, Adobe Acrobat DC 

To subscribe for Acrobat DC, you can check its plans and pricing: Plans and pricing | Adobe Acrobat DC

Thanks,

Akanchha

There are free 3rd party tools like PDFtk, PDF tool kit, that uses the command line or terminal mode to combine multiple PDFs into one PDF.

Not possible. You would need Adobe Acrobat or a subscription to Adobe PDF Pack.