Convert pdf to byte [] and vice versa ASP.NET MVC

I have to save a PDF in a field of a table in SQL Server 2016.

By informing me I have seen that the best way to do this is to convert it to byte []. The problem is that I do not finish to find a method that works for me, since I want to do it in the following way:

When I create a new record, from the Create view, I have a field that is to select the file of my computer that I want to save in the DB.

This is the code:

    @using (Html.BeginForm())
{
@Html.AntiForgeryToken()

<div class="form-horizontal">
    <h4>Compras</h4>
    <hr />
    @Html.ValidationSummary(true, "", new { @class = "text-danger" })
    <div class="form-group">

    </div>        <div class="form-group">
        @Html.LabelFor(model => model.empresaC, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.empresaC, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.empresaC, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.num_diarC, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.num_diarC, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.num_diarC, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.num_movC, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.num_movC, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.num_movC, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.mes_diarC, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.mes_diarC, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.mes_diarC, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.anno_diarC, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.anno_diarC, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.anno_diarC, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.codigoC, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.codigoC, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.codigoC, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.nombreC, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.nombreC, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.nombreC, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.num_factC, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.num_factC, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.num_factC, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.fec_factC, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.fec_factC, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.fec_factC, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.imp_factC, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.imp_factC, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.imp_factC, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.tiva_factC, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.tiva_factC, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.tiva_factC, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.kg_facC, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.kg_facC, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.kg_facC, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.obs_factC, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.obs_factC, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.obs_factC, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        @Html.LabelFor(model => model.imagenC, htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-4 btn">
            @Html.TextBoxFor(model => model.imagenC, new { type="file"})
            @Html.ValidationMessageFor(model => model.imagenC, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        <div class="col-md-offset-2 col-md-10">
            <input type="submit" value="Añadir" class="btn btn-default" />
        </div>
    </div>
</div>
}

What I want to know is how can I convert the file to byte [] when I select it in the Create view. And then how to convert it again (without having to download it) to display it in the Details view.

The code:

        <div class="col-md-4">
    <section>
        <iframe src="~/src/donquijote1.pdf" style="width:650px; height:700px;" frameborder="0" />
    </section>
</div>

Create statement:

            [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Create([Bind(Include = "idC,empresaC,num_diarC,num_movC,mes_diarC,anno_diarC,codigoC,nombreC,num_factC,fec_factC,imp_factC,tiva_factC,kg_facC,obs_factC,id_imagenC,imagenC")] ModelCompra compra)
    {
        Compra dbCompra = new Compra();

       if (ModelState.IsValid)
       {
            dbCompra = new ModelCompra().getDbCompra(compra);
            db.Compras.Add(dbCompra);
            try
            {
                db.SaveChanges();
            }
            catch (DbEntityValidationException ex)
            {
                foreach (DbEntityValidationResult item in ex.EntityValidationErrors)
                {
                    // Get entry

                    DbEntityEntry entry = item.Entry;
                    string entityTypeName = entry.Entity.GetType().Name;

                    // Display or log error messages

                    foreach (DbValidationError subItem in item.ValidationErrors)
                    {
                        string message = string.Format("Error '{0}' occurred in {1} at {2}",
                                 subItem.ErrorMessage, entityTypeName, subItem.PropertyName);
                    throw new DbEntityValidationException(message);
                }
            }
            }
            return RedirectToAction("Index");
        }
    return View(compra);
    }

The try / catch is because I had another problem and needed to expand the bug report