This post is about forgeries and pseudepigrapha in ancient times – whether merely alleged or actually proven, and whether alleged by ancient scholars or modern ones.
What the Ancients Thought About Forgeries
This is found in Forged: Writing in the Name of God – Why the Bible’s Authors Are Not Who We Think They Are (2011) by Bart D. Ehrman.
Most church leaders did not appreciate fabricated documents. But there were plenty to go around. (p. 18)
In short, there were long, protracted, and often heated debates in the early church over forged documents. Early Christians realized that there were numerous forgeries in circulation, and they wanted to know which books were written by their alleged authors and which were not. (p. 22)
Where Bart Ehrman and J. I. Packer Agree
Chapter 2 of Forged (titled “Alternatives to Lies and Deception”), Bart Ehrman writes (on p. 115):
Scripture says that it is inspired or breathed out by God. God does not and cannot lie. Therefore Scripture does not and cannot contain lies. Forgery, on the other hand, involves lying. For that reason there can be no forgeries in the Bible. This conservative evangelical view is still very much held by some scholars today, at least by conservative evangelical scholars. But I should emphasize it is a view that is built on theological premises of what has to be true , not on the grounds of what actually is true.
Ehrman marks an endnote right after “true” which reads (on p. 280):
A partial exception may be the view of evangelical scholar Donald Guthrie, who tries to argue on historical, rather than dogmatic, grounds that there can be no forgeries in the New Testament; see his “The Development of the Idea of Canonical Pseudipigrapha in New Testament Criticism,” Vox Evangelica 1 (1962): 43– 59.
Guthrie’s article can be found online here. In the article, Guthrie quotes J. I. Packer in this section:
Among those who during the period since the rise of criticism have maintained the rejection of canonical pseudepigrapha two different approaches may be discerned, the dogmatic and the historical. The former approach is well represented by a recent writer, J. I. Packer, who makes the following assertion, “We may lay down as a general principle that, when biblical books specify their own authorship, the affirmation of their canonicity involves a denial of their pseudonymity. Pseudonymity and canonicity are mutually exclusive.”  He goes on to assert that since the New Testament books were received into the canon, that must ipso facto rule out the possibility of pseudonymous authorship for any New Testament writing. “As we have seen, if a New Testament book is not authentically apostolic, and if it makes false assertions (as on this hypothesis these books do), then it has not the nature of Scripture, and has no place in the New Testament canon. But the fact is that these books established their place in the canon of the early Church, and have been studied and expounded in the Church for centuries without anything unworthy of their apparent authors, or inconsistent with the rest of Scripture, either in teaching or in tone, being found in them.” 
The footnotes are to Packer’s Fundamentalism and the Word of God (1958), pages 184 and 185, respectively. Guthrie goes on to say:
Packer argues strongly for the description of pseudonymous works as “forgeries”. He defines it as follows. “The dictionary definition of ‘forgery’ is fraudulent imitation, as such, irrespective of its aim, the point of the fraud being simply to get one’s own product accepted as somebody else’s”.  Moreover, in answer to those who postulate the highest motives, Packer maintains, “frauds are still fraudulent, even when perpetrated from noble motives”. The difficulty which arises here is that different minds have different notions of what is meant by “forgery”.
The footnotes are, again, to Packer’s book, this time pages 183 and 184, respectively.
Parenthetically, regarding Packer’s view let me add what I myself found in his book because it defines his position in the most pithy way:
Pseudonymity and canonicity are mutually exclusive. (p. 184)
…to deny authenticity is to deny canonicity also. (p. 186)
Having given Packer as his example of the “dogmatic” approach, Guthrie then goes on to give examples of the “historical” approach, which I’ll not reproduce here. Suffice it to say that while Guthrie may respect Packer’s theological justification for rejecting pseudonymous works, he considers historical justification “more enlightened.”
The primary point for our purposes is that while Ehrman emphatically rejects Packer’s theological views, the two men are in full agreement about the definition of forgery and that any pseudonymous work deserves that label whether it is in the New Testament canon or not. Thus Ehrman insists that the New Testament contains forgeries and Packer insists that it does not – both men fully agreeing on what constitutes a forgery.
Where Bruce Metzger Disagrees with Ehrman and Packer
Bruce Metzger wrote “Literary Forgeries and Canonical Pseudepigrapha” in Journal of Biblical Literature, Vol. 91, No. 1 (Mar., 1972), pp. 3-24.
The idea of pseudepigrapha being in the New Testament does not bother Metzger as it bothers Packer. Metzger begins his concluding paragraph with:
The recognized custom of antiquity allowed historians great freedom in representing the sentiments of those about whom they wrote by means of imaginary speeches, founded more or less on what was actually said. If, indeed, an entire book should appear to have been composed in order to present vividly the thoughts and feelings of an important person, there would not seem to be in this circumstance any reason to say that it could not be divinely inspired. Why, then, should inspiration be denied if, as in the case of 2 Peter (which most scholars believe was written about A.D. 125-140), the author appears to have drawn up the treatise in the name of Simon Peter (1:1) and with details lending a high degree of verisimilitude (e.g., the reference to having been present at the Transfiguration, 1:17-18) in order to recall second and third generation Christians back to the orthodox teaching and practice held to have been inculcated by Peter himself?
Metzger then concludes his essay with this sentence:
In short, since the use of the literary form of pseudepigraphy need not be regarded as necessarily involving fraudulent intent, it cannot be argued that the character of inspiration excludes the possibility of pseudepigraphy among the canonical writings.
While Packer would say that 2 Peter must have been written by Peter or else it wouldn’t be part of the New Testament canon, Metzger says it could still be canonical even if Peter didn’t write it, and Ehrman says that irrespective of its canonicity or lack thereof it was not written by Peter. Thus modern scholars argue amonst themselves while ancient scholars settled the matter long ago – in favor of Peter’s authorship.