Depends on what you want to include in your question.
Executables? .exe
Libraries? .dll
Log files? .log
Text files used to store Qlik script for inclusion in the script of apps? .qvs by convention, but could be anything or none.
CSV files used as data sources? .csv
Text files used as data sources .... could end with any extension or none
Excel files used as data sources? .xls or .xlsx
Image files in content libraries? .png, .jpg, .jpeg, .gif
etc... etc...
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