let enumerator = FileManager.default.enumerator(atPath: folderPath)
let filePaths = enumerator?.allObjects as! [String]
let txtFilePaths = filePaths.filter{$0.contains(".txt")}
for txtFilePath in txtFilePaths{
//Here you get each text file path present in folder
//Perform any operation you want by using its path
}
let documentsPath = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0]
let url = URL(fileURLWithPath: documentsPath)
let fileManager = FileManager.default
let enumerator: FileManager.DirectoryEnumerator = fileManager.enumerator(atPath: url.path)!
while let element = enumerator.nextObject() as? String, element.hasSuffix(".txt") {
// do something
}