Use a while loop for this purpose like below
NSFileManager *manager = [NSFileManager defaultManager];
int i = 1;
NSArray *documentPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentPath = [documentPath objectAtIndex:0];
NSString *newFileName = [documentPath stringByAppendingPathComponent:@"simpleFile.txt"];
while ([manager fileExistsAtPath:newFileName]) {
NSString *testName = [NSString stringWithFormat:@"simpleFile%d.txt", i];
newFileName = [documentPath stringByAppendingPathComponent:testName];
i++;
}