No SearchAttachmentText or SearchAttachment field for indexed PDF documents

Using

EPiServer.Find 13.0.1

EPiServer.Find.Cms.AttachmentFilter 13.0.1

And I have installed the Adobe PDF iFilter 64 11.0.01 on my laptop and restarted.

PDF files are stored as a type called TextBasedMedia when uploaded to the Episerver media folder.

[ContentType(GUID = "31F37C34-895D-4F39-BA8C-78FC1741E854")]
[MediaDescriptor(ExtensionString = "txt,pdf,doc,docx,ppt,pptx,xls,xlsx")]
[IndexInContentAreas]
public class TextBasedMedia : GenericMedia 
{}
// And GenericMedia is...
public class GenericMedia : MediaData
{
     /// <summary>
     /// Gets or sets the description.
     /// </summary>
     public virtual String Description { get; set; }
}

When inspecting TextBasedMedia in the index I cant't see any readable content from the PDF-file 

SearchAttachmentText$$String is missing 

as is SearchAttachment$$Attachment

Shouldn't there be a SearchAttachmentText$$String field at least?

I have cleared and re-indexed my developer index.

I'm able to perform a free-text search and get relevant hits matching text inside the indexed PDF-files using UnifiedSearch.

But as I understand I would get a better search relevancy using the attachment helper (EPiServer.Find.Cms.AttachmentFilter)?

What am I missing?