As @Jon Skeet said, you can use iTextSharp (which is a C# port of the Java iText).
First, download iTextSharp (currently 5.1.2), extract itextsharp.dll to some location and add a reference to it in Visual Studio. Then use the following code which is a full-working WinForms app that creates a very basic table in an A4 document. See the comments in the code for more of an explanation.
using System;
using System.Text;
using System.Windows.Forms;
using System.IO;
using iTextSharp.text;
using iTextSharp.text.pdf;
namespace Full_Profile1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            //This is the absolute path to the PDF that we will create
            string outputFile = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Desktop), "Sample.pdf");
            //Create a standard .Net FileStream for the file, setting various flags
            using (FileStream fs = new FileStream(outputFile, FileMode.Create, FileAccess.Write, FileShare.None))
            {
                //Create a new PDF document setting the size to A4
                using (Document doc = new Document(PageSize.A4))
                {
                    //Bind the PDF document to the FileStream using an iTextSharp PdfWriter
                    using (PdfWriter w = PdfWriter.GetInstance(doc, fs))
                    {
                        //Open the document for writing
                        doc.Open();
                        //Create a table with two columns
                        PdfPTable t = new PdfPTable(2);
                        //Borders are drawn by the individual cells, not the table itself.
                        //Tell the default cell that we do not want a border drawn
                        t.DefaultCell.Border = 0;
                        //Add four cells. Cells are added starting at the top left of the table working left to right first, then down
                        t.AddCell("R1C1");
                        t.AddCell("R1C2");
                        t.AddCell("R2C1");
                        t.AddCell("R2C2");
                        //Add the table to our document
                        doc.Add(t);
                        //Close our document
                        doc.Close();
                    }
                }
            }
            this.Close();
        }
    }
}