Thousands of pages of Hillary Clinton’s official records are set to be released in coming weeks, testing the Democratic presidential candidate as she looks to maintain her advantage in the final two months of the campaign.

On the heels of recently released Federal Bureau of Investigation documents on Mrs. Clinton’s use of a private email account at the State Department, the coming disclosures are likely to provide fodder for Republican Donald Trump. While Mrs. Clinton has held a durable if narrower lead over her rival in polls,...