namespace ConvertWebPageToPDFLinkWebPart.VisualWebPart1
{
    public class Utils
    {
        public static string API_KEY = "--ADD-YOUR-PDF-CO-API-KEY-HERE--";
    }
}

using Microsoft.SharePoint;
using Microsoft.SharePoint.WebControls;
using System;
using System.ComponentModel;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;

namespace ConvertWebPageToPDFLinkWebPart.VisualWebPart1
{
    [ToolboxItemAttribute(false)]
    public class VisualWebPart1 : WebPart
    {
        // Visual Studio might automatically update this path when you change the Visual Web Part project item.
        private const string _ascxPath = @"~/_CONTROLTEMPLATES/15/ConvertWebPageToPDFLinkWebPart/VisualWebPart1/VisualWebPart1UserControl.ascx";

        protected override void CreateChildControls()
        {
            var control = (VisualWebPart1UserControl)Page.LoadControl(_ascxPath);
            Controls.Add(control);

            control.CurrentWeb = SPContext.Current.Web;
        }
    }
}

using Microsoft.SharePoint;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using System;
using System.Collections.Generic;
using System.IO;
using System.Net;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;

namespace ConvertWebPageToPDFLinkWebPart.VisualWebPart1
{
    public partial class VisualWebPart1UserControl : UserControl
    {
        public SPWeb CurrentWeb { get; set; }

        // The authentication key (API Key).
        // Get your own by registering at https://app.pdf.co
        string API_KEY = Utils.API_KEY;

        // Destination PDF file name
        const string DestinationFile = "result.pdf";
        const string DestinationLibName = "Shared Documents";

        protected void Page_Load(object sender, EventArgs e)
        {
        }

        protected void StartButton_Click(object sender, EventArgs e)
        {
            // Create standard .NET web client instance
            ServicePointManager.Expect100Continue = true;
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
            WebClient webClient = new WebClient();
            var SourceUrl = UrlTextBox.Text;

            if (String.IsNullOrWhiteSpace(SourceUrl))
            {
                LogTextBox.Text += "Enter valid web page url \n";
                return;
            }

            // Set API Key
            webClient.Headers.Add("x-api-key", API_KEY);
            
            // URL for `Web Page to PDF` API call
            string url = "https://api.pdf.co/v1/pdf/convert/from/url";

            // Prepare requests params as JSON
            Dictionary<string, object> requestBody = new Dictionary<string, object>();
            requestBody.Add("name", DestinationFile);
            requestBody.Add("url", SourceUrl);

            // Convert dictionary of params to JSON
            string jsonPayload = JsonConvert.SerializeObject(requestBody);

            try
            {
                // Execute POST request
                var response = webClient.UploadString(url, "POST", jsonPayload);

                // Parse JSON response
                JObject json = JObject.Parse(response);

                if (json["error"].ToObject<bool>() == false)
                {
                    // Get URL of generated PDF file
                    string resultFileUrl = json["url"].ToString();

                    // Download PDF file
                    var retData = webClient.DownloadData(resultFileUrl);

                    //Upload file to SharePoint document library
                    //Read create stream
                    using (MemoryStream stream = new MemoryStream(retData))
                    {
                        //Get handle of library
                        SPFolder spLibrary = CurrentWeb.Folders[DestinationLibName];

                        //Replace existing file
                        var replaceExistingFile = true;

                        //Upload document to library
                        SPFile spfile = spLibrary.Files.Add(DestinationFile, stream, replaceExistingFile);
                        spLibrary.Update();
                    }

                    LogTextBox.Text += String.Format("Generated PDF document saved as \"{0}\\{1}\" file. \n", DestinationLibName, DestinationFile);
                }
                else
                {
                    LogTextBox.Text += json["message"].ToString() + " \n";
                }
            }
            catch (Exception ex)
            {
                LogTextBox.Text += ex.ToString() + " \n";
            }

            webClient.Dispose();

            LogTextBox.Text += "\n";
            LogTextBox.Text += "Done...\n";
        }
    }
}

//------------------------------------------------------------------------------
// <auto-generated>
//     This code was generated by a tool.
//
//     Changes to this file may cause incorrect behavior and will be lost if
//     the code is regenerated. 
// </auto-generated>
//------------------------------------------------------------------------------

namespace ConvertWebPageToPDFLinkWebPart.VisualWebPart1
{


    public partial class VisualWebPart1UserControl
    {

        /// <summary>
        /// UrlTextBox control.
        /// </summary>
        /// <remarks>
        /// Auto-generated field.
        /// To modify move field declaration from designer file to code-behind file.
        /// </remarks>
        protected global::System.Web.UI.WebControls.TextBox UrlTextBox;

        /// <summary>
        /// StartButton control.
        /// </summary>
        /// <remarks>
        /// Auto-generated field.
        /// To modify move field declaration from designer file to code-behind file.
        /// </remarks>
        protected global::System.Web.UI.WebControls.Button StartButton;

        /// <summary>
        /// LogTextBox control.
        /// </summary>
        /// <remarks>
        /// Auto-generated field.
        /// To modify move field declaration from designer file to code-behind file.
        /// </remarks>
        protected global::System.Web.UI.WebControls.TextBox LogTextBox;
    }
}