What happens if a patent application is filed with informal papers?

If a patent application is filed with informal papers (e.g., typed on both sides of the paper, not permanent, legible, or reproducible), the USPTO will still accord a filing date if the application otherwise meets the requirements. The MPEP states:

OPAP accords a filing date, as of the date indicated by the “Office Date” stamp (see MPEP § 505), to application papers which include a specification containing a description and at least one claim (nonprovisional applications filed under 37 CFR 1.53(b) prior to March 18, 2013 and design applications), and a drawing, if necessary under 35 U.S.C. 113 (first sentence) and 37 CFR 1.53(b), but are informal because they do not comply with the rules or notices.

The USPTO will send a Notice requiring correction of the informality. Failure to correct the informality within the specified time will result in abandonment of the application.