"I am reading the historical newspaper."

Translation: Táim ag léamh an nuachtáin stairiúil.

[ThDonaghey]

And it's "nuachtáin" not "nuachtán" here because... ? (I'm light on the grammar, I know; this is really my entry into Irish.)

[scilling]

… because a verbal noun requires the genitive case in a following noun. (The adjective is also in genitive case, but stairiúil happens to be the same in the genitive case for masculine nouns.)

[LeeInCalif]

Scilling has it spot on. In the tips for the Verbal Noun skill, there's a section on "objects after a verbal noun" that includes some helpful examples.