PDF is larger than 104.9 MB, so it cannot be combined

Greetings. I just signed up for the Adobe Acrobat subscription service on my iPad Pro using the app, so that I could combine files needed for work, but apparently a few of these files are too big, according to the error in the subject title. ".pdf is larger than 104.9 MB, so it cannot be combined." It's rather imperative I get these files combined, even if they are "too large." I currently have 441.7 GB of storage available on my iPad. Is there any way around this restriction? What causes the restriction? I hope to continue the subscription if the app works as solicited. 

Any help would be much appreciated