Understanding all output files when compiling a LaTeX document

Question

I've been using MiKTeX for a while, but I haven't really understood what all the output files are. I'm using pdflatex and I've just started using biber for bibliography. When I compile a .tex file I get 9 output files. These 2 I understand:

• .pdf
• .log

But I didn't really grasp what is the function of these 7:

• .synctex.gz
• .aux
• .bbl
• .bcf
• .blg
• .out
• .run
• .xml

Answer 1

• .synctex.gz: Synctex stores a correspondence between the output PDF and the .tex source. Some editors use it to show your cursor position in the PDF or PDF scroll position in the .tex source. See What exactly is SyncTeX?

• .aux: Open it in a text editor, you'll see this file is used mostly for reference information.

  For example, if you use \ref{} but the corresponding \label{} is only later in the document, LaTeX has not seen it, and won't look ahead. Instead, each time there is a \label{}, a command gets written to the .aux file. Next time you compile your .tex, that .aux is inputted right before the document gets started, and the command you had written to it then registers the value for \ref{}.

• .toc (bonus): If you use \tableofcontents, this will create a .toc file as well, because just as for the .aux file: there is no looking ahead. The .toc records a \contentsline for each section encountered. Upon use of \tableofcontents, this file is inputted, and each \contentsline constitutes a line in the contents table.

• .bbl: Is outputted by biber (or bibtex), contains the prepared data to be used by biblatex (or natbib).

• .bcf: Is outputted by biblatex (or natbib), contains which citations biber (or bibtex) should prepare.

• .blg: The log file of biber (or bibtex).

• .out: Used by hyperref to store a list of PDF bookmarks. Note how the information can differ from that in .toc. For example when adding \pdfbookmark without a corresponding one for the TOC, or when using \texorpdfstring. This latter one allows for a different title in the PDF toc. See the following example:

  \section[\texorpdfstring{I'm in document toc!}{I'm in PDF toc!}]{I'm in \TeX!}
  \section{I'm in \texorpdfstring{\TeX{} or toc! $\cos(\theta)$}{PDF toc! cos(\texttheta)}}
  

  You see \texorpdfstring string can be used to provide a fallback for math, which can't be typeset in a PDF toc. I'm using the package \textgreek here.

• .run.xml: The header of this file contains "logreq request file". According to CTAN, this package logs a couple of useful messages, like "please rerun LaTeX". (https://www.ctan.org/pkg/logreq)