There’s no such thing.
Link me to it then.
It apparently is, since the paper you cited was from a university known as a bastion of liberalism within the RCC, due to its associations with the Jesuits.
Regarding the question of an imprimatur for the work, upon some research, I am not so sure if the book ever received an imprimatur.
So, for some background. Samuele Bacchiocchi, again, was a Seventh Day Adventist who attended Pontifical Gregorian University, being the first non-Catholic to ever do so. As his dissertation for graduation, he wrote a wrote on the change of Sabbath to Sunday. This dissertation was later revised into a book called From Sabbath to Sunday, and it is alleged it received an imprimatur from the Catholic Church, or at least the university he graduated from. How much an imprimatur is worth can be exaggerated (it inherently carries with it no more than the authority of the specific person or persons who grants it), but the question is: Did it receive one?
Now, I for quite a while assumed that this was given an imprimatur, but not a nihil obstat, on the grounds that... well, from what I remember when I looked at it (I got a copy temporarily quite a while ago because I was trying to look into something from it), the book
said there was an imprimatur at the start, but no mention of a nihil obstat. But it seems this might have been inaccurate, or at least misleading. So about two decades ago there arose a controversy about whether some of Bacchiocchi's claims about himself and his work were valid, such as whether he actually graduated from the university or received a gold medal from the pope, which got compounded by someone from the university claiming some of his claims were false. But then it turns out some of that person's claims weren't accurate. Some information about this can be found in this series of posts
here. On the specific question of the imprimatur, see particularly
this one and
this one; also see
the comments on this post (alluded to in the prior links). This last link should automatically bring you to the more relevant part, but the important things begin on comment #78 and go to #95). To be fair, these are not from the most friendly of witnesses towards Bacchiocchi, though their points do seem valid to me (and they do note how a bunch of the accusations towards Bacchiocchi were false).
I'll try to summarize things. As noted, Bacchiocchi got cleared of a lot of the accusations, but most of them don't concern us, and the one that does is where things get more murky, and it's about the imprimatur. Based on the information from those posts, and reading Bacchiocchi's defenses (linked to from the above post), it looks to me like his book From Sabbath to Sunday never got any imprimatur. What got an imprimatur--though it seems it might have been an imprimi potest from the university rather than an more formal imprimatur--was an abridged version of his dissertation. This imprimatur (or imprimi potest, whichever it was) of a major portion of the dissertation was a requirement for graduation. This abridged version of the dissertation was called "Anti-Judaism and the Origin of Sunday". Apparently to get the imprimi potest, he had to get the university to do it, because his local bishop declined to give his work an imprimatur (it is not clear to me whether this refusal was for the abridged or unabridged version of his dissertation).
At any rate, the university give imprimi potest to "Anti-Judaism and the Origin of Sunday". Bacchiocchi then wrote "From Sabbath to Sunday", based on his dissertation, and published that. The problem is, whatever weight the original imprimi potest for "Anti-Judaism and the Origin of Sunday" could have had did not apply to this one, it being a different work. Despite this, it was printed with the imprimi potest of the original work at the start of the book, albeit it now said "imprimatur". I do not think this was done deliberately dishonestly by Bacchiocchi--these distinctions would no doubt be confusing to a non-Catholic, and by his account it seems his professor led him to think a new imprimatur wasn't necessary for his work--but at the end of the day, it means an imprimi potest for one work is misleadingly being applied as an imprimatur to a separate, albeit related, work.
I do not have copies of them available to me right now (the closest library that has From Sabbath to Sunday is an hour away, and the closest that has Anti-Judaism and the Origin of Sunday is even farther), so I cannot try to gauge how much was different between these works, and thus if perhaps "Anti-Judaism and the Origin of Sunday" was much more tempered in its statements, which could have gotten it the permission. But at any rate, an imprimi potest on one work does not automatically transfer to another one.
For the record, Bacchiocchi appears to not claim that the imprimatur (if it was that rather than an imprimi potest) was an actual sanction of the church, at least if the e-mail quoted from
here is legitimate (I obviously have no way to verify the validity of a private e-mail quote):
Regarding the imprimatur, he [Ghirlanda] explains that the approval that I received from granted by the Gregorian University, not by the Catholic church at large.
So based on the information I can gather, it appears that it is highly misleading to claim that Bacchiocchi's "From Sabbath to Sunday" was ever granted any kind of imprimatur by the Catholic Church. The imprimi potest or imprimatur (whichever it was) was granted by the university. Furthermore, this did
not apply to "From Sabbath to Sunday", but rather an earlier, though similar, work called "Anti-Judaism and the Origin of Sunday".
As for whether Bacchiocchi's arguments in From Sabbath to Sunday are good or not, I can't say, having again no present access to the work. I read a little of it a while ago--someone cited it for something so I got a copy from a library loan in order to look at that specific thing--but not enough to try to give anything close to a full appraisal of it. But my interest is not in whether the work is well argued or persuasive, but simply whether it had an imprimatur--which, for the reasons noted above, it does not appear it did.
