With a footnote reading "with acknowledgments to...........".
Using others' work without proper attribution can be considered plagiarism or even fraud.
it is most important if you are quoting someone or something that they wrote, so that when you do, you won't be caught for plagerism.
Include a citation to acknowledge an outside source whenever the outside source information is used in the paper.
A primary source can be letters, diaries/journals (for those males out there), documents, speeches, interviews, and even photographs!