Nothing would prevent someone from using any ordinary desktop publishing software to fabricate a tax return and fill in fictitious numbers. In fact, I wouldn't be shocked if these media outlets receive dozens of such things every month ... 1099 forms for Donald Trump from "Vladimir Putin," invoices for construction services at a Trump property in the Middle East from "Osama bin Laden," etc.
The reporter had to have some way of verifying the accuracy of the information he received.
P.S. -- Why would you assume that the reporter was telling the truth about how he got the document, anyway?
You’re just creating more supposition where there is none. The reporter said he got it “thus and thus” and now you posit that “they” knew all along what and where it came from. Both patently cannot be true. I don’t buy it.
As for just the front pages, that’s all that’s needed. It shows the income, the deductions, AGI, and the taxes. The rest is merely backup to justify the primary numbers on the main form.