This is pdfTeX, Version 3.14159265-2.6-1.40.19 (TeX Live 2019/dev/Debian) (preloaded format=pdflatex 2019.6.1) 10 JUN 2019 19:14 entering extended mode restricted \write18 enabled. %&-line parsing enabled. **conclusion.tex (./conclusion.tex LaTeX2e <2018-12-01> ! Undefined control sequence. l.1 \section {Conclusion and future plans} The control sequence at the end of the top line of your error message was never \def'ed. If you have misspelled it (e.g., `\hobx'), type `I' and the correct spelling (e.g., `I\hbox'). Otherwise just continue, and I'll forget about whatever was undefined. ! LaTeX Error: Missing \begin{document}. See the LaTeX manual or LaTeX Companion for explanation. Type H <return> for immediate help. ... l.1 \section{C onclusion and future plans} You're in trouble here. Try typing <return> to proceed. If that doesn't work, type X <return> to quit. Missing character: There is no C in font nullfont! Missing character: There is no o in font nullfont! Missing character: There is no n in font nullfont! Missing character: There is no c in font nullfont! Missing character: There is no l in font nullfont! Missing character: There is no u in font nullfont! Missing character: There is no s in font nullfont! Missing character: There is no i in font nullfont! Missing character: There is no o in font nullfont! Missing character: There is no n in font nullfont! Missing character: There is no a in font nullfont! Missing character: There is no n in font nullfont! Missing character: There is no d in font nullfont! Missing character: There is no f in font nullfont! Missing character: There is no u in font nullfont! Missing character: There is no t in font nullfont! Missing character: There is no u in font nullfont! Missing character: There is no r in font nullfont! Missing character: There is no e in font nullfont! Missing character: There is no p in font nullfont! Missing character: There is no l in font nullfont! Missing character: There is no a in font nullfont! Missing character: There is no n in font nullfont! Missing character: There is no s in font nullfont! Overfull \hbox (20.0pt too wide) in paragraph at lines 1--2 [] [] ! LaTeX Error: Missing \begin{document}. See the LaTeX manual or LaTeX Companion for explanation. Type H <return> for immediate help. ... l.3 T ODO You're in trouble here. Try typing <return> to proceed. If that doesn't work, type X <return> to quit. Missing character: There is no T in font nullfont! Missing character: There is no O in font nullfont! Missing character: There is no D in font nullfont! Missing character: There is no O in font nullfont! ) ! Emergency stop. <*> conclusion.tex *** (job aborted, no legal \end found) Here is how much of TeX's memory you used: 5 strings out of 492615 154 string characters out of 6131391 57402 words of memory out of 5000000 4018 multiletter control sequences out of 15000+600000 3640 words of font info for 14 fonts, out of 8000000 for 9000 1141 hyphenation exceptions out of 8191 5i,0n,4p,54b,16s stack positions out of 5000i,500n,10000p,200000b,80000s ! ==> Fatal error occurred, no output PDF file produced!