From LimeSurvey Manual
Outdated translations are marked like this.
Allowed file types (allowed_filetypes)
You may enter in this field the file types that are allowed to be uploaded by the respondent as answer to the question. The file formats must be separated by a comma.
- One may enter: JPG, jpeg, png, gif.
When checking the allowed file types, LimeSurvey check extension and mime type. Default system know common mime types. If you need specific file type, you have to update your config.php file.