Add attachment filed column in SharePoint custom list forms through SharePoint designer 2013

1. Open the Custom Form (either it is edit or new item) in the SharePoint Designer 2010/2013.
   
2. Identify the place and paste the following code in SPD. 

<tr>  
   <td rowspan="2" width="190px" valign="top" height="50px">  
      <H3>  
         Upload Evidence  
      </H3>  
   </td>  
   <td valign="bottom" height="15" id="attachmentsOnClient">  
      <span dir="ltr">  
         <input type="file" name="fileupload0" id="onetidIOFile" size="56" title="Name" />  
      </span>  
   </td>  
</tr>  
<tr>  
<td colspan="4">  
   <input id="attachOKbutton" type="BUTTON" onclick='OkAttach()' value="Upload" style="width: 12.8em; height: 2em"/>  
   <span id="idSpace"/>  
</td>  
</tr>