Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Seventh Ecumenical Council.  The Second Council of Nice.: Section II

II.  Authority of the Caroline Books.

But be their authorship what it may, we come next to consider their authority; and here we are met with the greatest difficulty, for it is certain that despite the statements to the contrary, these books were not those sent to Pope Hadrian by Charlemagne, those of which the Pope deigned to write a refutation.  This Hefele has clearly proved, by pointing out that those sent to the Pope treated the matter in an entirely different order; that there were in those sent only 85 chapters, while these books have 120 (or 121 if the authenticity of the last chapter is granted).  Moreover the quotations made by Hadrian do not occur verbatim in the Caroline books, but are in some cases enlarged, in others abbreviated.  (Cf. Hefele’s treatment of the whole subject in the original German.)  Petavius thinks that what Hadrian received were extracts from the Caroline Books, made by the Council of Frankfort.

p. 579 Hefele arrives at a directly opposite conclusion, viz., that the Caroline Books are an expansion of the Capitula sent to the Pope, and that this expansion was made at the bidding of Charlemagne.

It should be noted here that Baronius, Bellarmine, Binius, and Surius all question the authenticity of the Caroline Books altogether.  (Vide Baron, Annal., a.d., 794.)  But this extreme position seems to be refuted by the fact that certain quotations made by Hincmar are found in the books as we have them.  (Cf. Sirmond in Mansi, Tom. XIII., 905, Labbe, Tom. VII., col. 1054.)