List<string> Temp = new List<string>();
string[] filePaths = Directory.GetFiles(@"C:\Temp\", "*.txt");

foreach (string files in filePaths)
{
    var fileStream = new FileStream(files, FileMode.Open, FileAccess.Read);
    using (var streamReader = new StreamReader(fileStream, Encoding.UTF8))
    {
        Temp.Add(streamReader.ReadToEnd());
    }
}

foreach (string i in Temp)
{
    if (i.Contains("Events"))
    {
        Console.WriteLine(i);
    }
}

"[Output]"
"[Events]"
"Time"  "Duration"  "Severity"  "Event" "Text1" "Text2"


"[Acquisition Settings_1]"
"Data Set"  "DataSet1"
"Data Stream"   "Data"


"[Scan Data (Pressures in Torr)]"
"Time"  "Scan"  "Mass 1"    "Mass 2"    "Mass 3"
"10/25/2018 4:59:27 PM" 1   5.5816e-008 1.3141e-008 -1.6109e-010
"10/25/2018 4:59:35 PM" 2   5.5484e-008 1.3403e-008 6.9720e-010
"10/25/2018 4:59:41 PM" 3   5.5633e-008 1.3388e-008 8.8094e-011
"10/25/2018 4:59:48 PM" 4   5.7289e-008 1.2343e-008 1.4095e-010
"10/25/2018 4:59:54 PM" 5   5.2841e-008 1.3219e-008 7.5257e-010

"10/25/2018 4:59:57 PM" "After Calibration due to marginal data of daily pm3 rga checking"
"10/25/2018 5:49:51 PM" "RGA Base Pressure
Flat pallet (2018-10-25_011_a1a)"
"10/25/2018 6:21:53 PM" "PM3 SiNFILL_27A
2018-10-25_011_A4A"
"10/25/2018 9:51:29 PM" "IBE1 STEP
FULL TAPE
NO PRE-BAKE"
"10/25/2018 9:58:48 PM" "IBE2 STEP

"10/25/2018 4:59:27 PM" 1   5.5816e-008 1.3141e-008 -1.6109e-010
"10/25/2018 4:59:35 PM" 2   5.5484e-008 1.3403e-008 6.9720e-010
"10/25/2018 4:59:41 PM" 3   5.5633e-008 1.3388e-008 8.8094e-011
"10/25/2018 4:59:48 PM" 4   5.7289e-008 1.2343e-008 1.4095e-010
"10/25/2018 4:59:54 PM" 5   5.2841e-008 1.3219e-008 7.5257e-010

^"d+/d+/d+ d+:d+:d+ (AM|PM)" -?ds+d+.?d+e-d+ -?d+.?d+e-d+ -?d+.?d+e-d+

var pattern = @"^""d+/d+/d+ d+:d+:d+ (AM|PM)"" -?ds+d+.?d+e-d+ -?d+.?d+e-d+ -?d+.?d+e-d+";

var regex = new Regex(pattern, RegexOptions.Compiled);

var results = File.ReadLines(@"D:Weird.txt").Where(x => regex.IsMatch(x));

foreach (var result in results)
   Console.WriteLine(result);

"10/25/2018 4:59:27 PM" 1   5.5816e-008 1.3141e-008 -1.6109e-010
"10/25/2018 4:59:35 PM" 2   5.5484e-008 1.3403e-008 6.9720e-010
"10/25/2018 4:59:41 PM" 3   5.5633e-008 1.3388e-008 8.8094e-011
"10/25/2018 4:59:48 PM" 4   5.7289e-008 1.2343e-008 1.4095e-010
"10/25/2018 4:59:54 PM" 5   5.2841e-008 1.3219e-008 7.5257e-01