In the Zotero import format settings choose
- BibTeX if your document uses classical BibTeX to produce the bibliography and
biblatex if you document uses biblatex to produce the bibliography.
Of course now the new questions are
Should you choose biblatex or BibTeX to produce the bibliography for a new document that doesn't already have a bibliography set up.
How you can tell which method an existing document with bibliography uses.
Question 1 is basically addressed by bibtex vs. biber and biblatex vs. natbib: biblatex has some extremely useful features and is generally seen as easier to customise than BibTeX, but if there is an existing BibTeX style that does what you want or you need to submit your work to a publisher, there is usually no reason to switch to biblatex. (How do I add "citations" at the end of the document as done here? and What to do to switch to biblatex? have extensive guidance on setting up the bibliography with the different available methods.)
It emerged in the comments that question 2 is what you are dealing with.
The following hints should help you figure out if a document you are looking at uses biblatex or BibTeX.
In an ideal world it would be easy to tell what bibliography method you document uses. A short look at the accepted answer to What to do to switch to biblatex? shows that a biblatex document loads the package biblatex, while a BibTeX-based bibliography approach definitely does not load that package.
If you document loads the package biblatex (as in \usepackage[...<some options>...]{biblatex}), then you use biblatex.
- The styles of the
biblatex-chicago bundle are usually loaded via the wrapper package biblatex-chicago, so if your document has \usepackage[...<some options>...]{biblatex-chicago}, you are also using biblatex.
Unfortunately, not all packages that are used in a document are loaded directly in the preamble. Packages can be loaded by other packages and templates often externalise parts of the preamble into other files, so it can be hard to figure out exactly what packages are loaded.
- To check if a package is loaded, you can add the command
\listfiles to the very top of your document. Then LaTeX will print a list of used packages at the end of the .log file. If biblatex is listed there, your document uses biblatex.
Investigations into loaded packages can be a bit tedious if you have no access to the .log files, so here are some other easy markers that can help you figure out which method your document uses.
If your document uses the command \addbibresource{<basename of bib file>.bib}, then you are using biblatex. (biblatex still allows the legacy command \bibliography{<basename of bib file>}, so if you only have a \bibliography command in your document you can't immediately tell biblatex from BibTeX. But: see the next point.)
If \bibliography{<basename of bib file>} is used in the preamble, you are using biblatex. If \bibliography{<basename of bib file>} is used in the document body at the exact place where the bibliography is printed, your are using BibTeX.
If your document contains a \bibliographystyle instruction, you are using BibTeX.
In your case the \bibliographystyle{ACM-Reference-Format} is a clear sign that you are using BibTeX. Which style (ACM-Reference-Format) you use is irrelevant for the question of BibTeX vs biblatex, the only thing that matters is that you have a \bibliographystyle in your document at all.
biber, choose BibLaTeX. If you're using a journal's template, usually the documentation will tell you which to use (or has an example in the code that will make it clear which is expected). If you're not sure which to use, refer to the linked question. :-)bibliography{...}line at the end is\bibliographystyle{ACM-Reference-Format}. By googling (stackoverflow.com/questions/48411689/…) I found that it expects bibtex. I think you should make your comment into the answer; but if there is a way to tell the expected format from the document without googling the name of the format, that would be good to have in the answer.