SF_10.1, SF_10.2, SF_11.0, SF_11.1, SF_11.2, SF_12.0, SF_12.1, SF_12.2, SF_13.0, SF_13.1, SF_13.2, SF_13.3, SF_14.0, SF_14.1, SF_14.2, SF_14.3 - https://docs.sitefinity.com/for-developers-get-formfield-content-links-from-submitted-form-responses

GetFormFieldContentLinksFromFormResponses.cs

using System.Linq;
using Telerik.Sitefinity.Forms.Model;
using Telerik.Sitefinity.Model;
using Telerik.Sitefinity.Model.ContentLinks;
using Telerik.Sitefinity.Modules.Forms;
using Telerik.Sitefinity.Modules.Libraries;

namespace Telerik.Sitefinity.Documentation.CodeSnippets.DevGuide.SitefinityEssentials.Modules.Forms
{
    public partial class FormsSnippets
    {
        public static void GetFormFieldContentLinksFromFormResponses(string formName, string formFieldName)
        {
            FormsManager formsManager = FormsManager.GetManager();
            LibrariesManager librariesManager = LibrariesManager.GetManager();

            //Get the Form by Name
            var form = formsManager.GetForms().Where(f => f.Name == formName).SingleOrDefault();

            //Get the FormEntries for that Form
            var records = formsManager.GetFormEntries(form);

            // Loop through all the response records for this form
            foreach (FormEntry record in records)
            {
                //Use GetValue() to obtain the fields ContentLink array
                var contentLink = record.GetValue<ContentLink[]>(formFieldName).FirstOrDefault();
                if (contentLink != null)
                {
                    var document = librariesManager.GetDocument(contentLink.ChildItemId);
                }
            }
        }
    }
}