Aside: I'm also curious about whether statements/questions like, "I'm curious about..." require a question mark after them.
I've googled the paper and the authors, and I've scoured the UTexas Law site, and turned up nothing. So, my best guess: perhaps it's wordplay: pretend < Latin pre- "before" + tendo "I stretch out; I reach for; I pitch; I offer" vs. foregive (now a homophone of forgive but originally having a slightly different meaning[1]). Thus "pretend paper" ≡ "foregive paper" ~ "forgive paper". It's a stretch, but it's all I can come up with...
[1]: fore- having a sense of "forward; before" whereas for-, being related to the "fro" in "to and fro", originally having a since of "away from". Now that "for" and "fore" are homophones, the two are conflated, but not for the first time in history: there were once three prefixes, which would've been fore-, for-, and fro- today had the latter two not already merged before the Anglo-Saxons even began writing. They corresponded to Latin pre-, per-, and pro-, respectively. Now there's one prefix, variously spelled, with various senses, however sometimes the senses are distinguished in writing by one spelling or another.
I meant to answer this, too, but I was being summoned and hit that reply button without thinking.
The answer is a little complicated, because orthographic rules are ultimately arbitrary. I've opted for detail to explain and support my answer, but you can skip to the last paragraph if you don't care for such things ;)
English orthography is subject to many de facto standards. A couple that are well-recognized are British vs. American spelling conventions, but even those are merely de facto rather than formally standardized by some regulatory institution as has been done for some other languages. And that's just spelling.
Punctuation is even more variable. Punctuation rules are usually given in "style guides", which are then variously adopted by publishers as official house style. In the US alone, I counted 11 different style guides popular enough to have nicknames. Eleven. However, I doubt they differ markedly in their punctuation rules, because publications seem to be fairly consistent.
The only one I have an actual copy of is the MLA Handbook (6th edition). It pedantically argues that the only permissible place for a question mark is the very end of an interrogative sentence (§3.2.11).
I argue, though, that such statements as yours are however semantically interrogative: they use the indicative mood, but most readers will pragmatically infer that they are requests for information. What yields answers? Questions. What do you do when you want answers? Ask questions. Then is anything said in hope of an answer akin to a question? For all intents and purposes, I'd say so.
Punctuation is just a tool that we use to help us communicate more effectively by writing. And that's not just my opinion—the MLA Handbook agrees (§3.2.1):
The primary purpose of punctuation is to ensure the clarity and readability of writing. Punctuation clarifies sentence structure, separating some words and grouping others. It adds meaning to written words and guides the understanding of readers as they move through sentences.
Let's look at your sentence, then:
> I'm curious about why the filename for the PDF is "Pretend-Paper.pdf"?
Here's how I perceive that question mark. It acts as a sort of prompt for an answer. Were we speaking in person, there would likely be prosodic or nonverbal cues to perform the same role: perhaps a particular tone of voice, a pause, a facial expression, a gesture, …. Spoken, it would be obvious that you were expecting an answer. Written, I think perhaps most people would be inclined to pick up on it regardless, but in case they don't, the question mark clarifies it. In any case, the question mark encodes whatever prosodic or nonverbal cue(s) you might've said—it adds meaning that the words alone do not really carry. Seems to me that it satisfies the primary purpose of punctuation according to the MLA. As for me, I'd call it a good use of the tool.
If question marks were to be reserved only for phrases in the interrogative mood, they'd be pretty useless. Such phrases are already obviously questions—at least in English. Does that add any meaning. Does that guide the understanding. No, it adds only redundancy. That can be useful, sure. But it's not the primary purpose, now, is it.
So, no. The question mark is not required there. But it isn't wrong to put one there, either. Notwithstanding, if you're ever writing something to submit to a publisher who requests that submissions adhere to some style guide—follow the style guide, even if it's nonsense. Argue about it later, with your editor ;)