How to read from pdf file?

I am new to reading pdf using C# where I have below function in my project. How to recognize text position in pdf file?

Here _dblRect has 151.0, 696.0, 400.0, 500.0

_strFileName is txt file name.

Can someone explain how this function works?

private string fcnTextFromCrop(string _strFileName, double[] _dblRect, CAcroPDDoc _docOriginal, int _intPage)

        {

            string str = "";

            try

            {

                object jSObject = _docOriginal.GetJSObject();

                System.Type type = jSObject.GetType();

                object target = null;

                object[] args = new object[] { _intPage };

                target = type.InvokeMember("extractPages", BindingFlags.InvokeMethod | BindingFlags.Public | BindingFlags.Instance, null, jSObject, args);

                object[] objArray2 = new object[] { "Crop", 0, 0, _dblRect };

                type.InvokeMember("setPageBoxes", BindingFlags.InvokeMethod | BindingFlags.Public | BindingFlags.Instance, null, target, objArray2);

                object[] objArray3 = new object[] { _strFileName, "com.adobe.acrobat.plain-text" };

                type.InvokeMember("saveAs", BindingFlags.InvokeMethod | BindingFlags.Public | BindingFlags.Instance, null, target, objArray3);

                object[] objArray4 = new object[] { true };

                type.InvokeMember("closeDoc", BindingFlags.InvokeMethod | BindingFlags.Public | BindingFlags.Instance, null, target, objArray4);

                using (StreamReader reader = new StreamReader(_strFileName))

                {

                    str = reader.ReadToEnd();

                    reader.Close();

                }

                System.IO.File.Delete(_strFileName);

            }

            catch

            {

                str = "";

            }

            return str;

        }