MLA

Wescott, Glenway, 1901-1987. Picasso, Pablo. Box 404, folder 4268. n.d.. https://collections.library.yale.edu/catalog/2024258.

APA, 6th edition

Wescott, Glenway, 1901-1987. (["Box 404, folder 4268"])(n.d.)[Picasso, Pablo]. https://collections.library.yale.edu/catalog/2024258.