The name of the movie comes from the fact that on the year 2013, director Laura Poitras received an encrypted e-mail from a stranger who calls himself "Citizenfour", who was Snowden, offering her inside information about illegal wiretapping practices of the US National Security Agency (NSA) and other intelligence agencies.
Laura Poitras took many security precautions related to the film, described by military writer Peter Maass among others. She moved to Berlin, Germany after being detained repeatedly at border controls when entering the US. She edited the film in Germany after flying directly there from Hong Kong with the Snowden footage, to prevent the FBI from showing up with a search warrant for her hard drives. All the film footage is kept on encrypted drives with multiple levels of nested protection. The computer she uses for reading sensitive documents is separated from the internet by an air gap.
The Film Society of Lincoln Center (which selects films for the New York Film Festival) reported that Laura Poitras changed the location of the initial screening for the NYFF's selection committee several times, in case someone was tracking her movements. The committee was shown a rough cut that had sensitive material redacted, and the NYFF "had to keep the movie's inclusion in the festival under wraps until mid-September" and it was "kept out of festival schedules and documents until [they] could talk about it openly". The last-minute inclusion in the festival's main slate was an unprecedented event for the NYFF, and "tickets for both screenings sold out within just a few hours".
The film's ending credits unusually name several free software projects and security tools, without which "this film would not be possible". The programs named include Tor, Tails, Debian GNU/Linux, Off-the-Record Messaging, the GNU Privacy Guard, Truecrypt, and SecureDrop.
Edward Snowden used the number "4" for his code name because Thomas Drake, William Binney and J. Kirk Wiebe all tried to expose the NSA's mass surveillance before him; in his mind they were numbers 1-3.
Laura Poitras received several journalistic and humanitarian awards for reporting the Snowden disclosures depicted in the film, including the George Polk award (with Glenn Greenwald and Ewen MacAskill), the Ridenhour Truth-Telling Prize (with Edward Snowden) the Carl von Ossietzky medal for human rights (with Greenwald and Snowden), and the Henri Nannen Prize for Efforts for Independence of the Press.
As soon as Laura Poitras thought Edward Snowden was legit source in February 2013, she started using another computer, separate email addresses and only checking that email from locations that were away from her home because she wanted to maintain source protection.
Before coming out as a whistle-blower Edward Snowden had researched previous cases of leaks in NSA by Thomas Drake, William Binney and J. Kirk Wiebe extensively to try and avoid being silenced and having his life destroyed for even considering speaking out.