You should use wavefunction file as input file, such as .wfn, .mwfn, .fch, .molden and so on, see Section 2.5 of Multiwfn manual for introduction, and see beginning of Chapter 4 of Multiwfn manual on how to generate them by popular quantum chemistry codes.
By the way, ELF is not useful in visualizing weak interactions, I strongly recommend using the popular IGMH method for this purpose, see original paper of IGMH:
Tian Lu, Qinxue Chen, J. Comput. Chem., 43, 539–555 (2022) DOI: 10.1002/jcc.26812
(The supplemental material of this paper contains a very detailed tutorial of performing IGMH analysis via Multiwfn)
Also it is highly suggested to read my review article about existing methods of visualizing weak interactions:
Tian Lu, Qinxue Chen, Visualization Analysis of Weak Interactions in Chemical Systems (2023), Comprehensive Computational Chemistry, Vol. 2 pp. 240-264. Oxford: Elsevier. DOI: 10.1016/B978-0-12-821978-2.00076-3
(If you cannot access to it, please feel free to E-mail me)
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more context: the input file is a ligand-protein interaction, and I want to visualize and analyze the weak interactions observed.
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