Cannot implicitly convert type 'System.Collections.Generic.List' to 'System.Collections.Generic.IEnumerable

applicantdata is IEnumerable<APPLICANT>, in your select statement you are selecting anonymous type object using new keyword, that is why you can't convert it to IEnumerable<APPLICANT>.

You have to create a temporay class with your properties as in select statement and return IEnumerable of that class.

Like:

public class MyClass
{
  public APPLICANT applicant {get;set;}
  public Profile porfile {get;set;}
}

Then modify your function to return IEnumerable<MyClass> like

public IEnumerable<MyClass> GetApplicant()
{
    IEnumerable<MyClass> applicantdata = Cache.Get("applicants") as IEnumerable<MyClass>;
    IEnumerable<Profile> profiledata = Cache.Get("profiles") as IEnumerable<Profile>;

    IEnumerable<MyClass> applicantList;
    if (applicantdata == null)
    {

        applicantList = (from a in context.Profiles 
                             join app in context.APPLICANTs
                             on a.PROFILE_ID equals app.Profile_id into joined
                             from j in joined.DefaultIfEmpty()
                             select new MyClass //Change here
                                        {
                                           APPLICANT = j, 
                                           Profile = a,
                                        }).Take(1000);

               applicantdata = applicantList.AsEnumerable();



        if (applicantdata != null && applicantdata.Any())
        {
            Cache.Set("applicants", applicantdata, 30);
        }
    }
    return applicantdata;

}

You can't project to APPLICANT, since that appears to be a class generated through entity framework.