37 CFR 3.24: Requirements for documents and cover sheets relating to patents and patent applications.

(a) For electronic submissions: Either a copy of the original document or an extract of the original document may be submitted for recording. All documents must be submitted as digitized images in Tagged Image File Format (TIFF) or another form as prescribed by the Director. When printed to a paper size of either 21.6 by 27.9 cm (8 1/2 by 11 inches) or 21.0 by 29.7 cm (DIN size A4), the document must be legible and a 2.5 cm (one-inch) margin must be present on all sides.

(b) For paper or facsimile submissions: Either a copy of the original document or an extract of the original document must be submitted for recording. Only one side of each page may be used. The paper size must be either 21.6 by 27.9 cm (8 1/2 by 11 inches) or 21.0 by 29.7 cm (DIN size A4), and in either case, a 2.5 cm (one-inch) margin must be present on all sides. For paper submissions, the paper used should be flexible, strong white, non-shiny, and durable. The Office will not return recorded documents, so original documents must not be submitted for recording.