I came across this issue the other day, you cannot add a rich text column to a document library, this was frustrating as I wanted to use the column to hold multiple html hyperlinks.
After doing some research I found this post on SharePoint Blogs –
It is possible to use a rich text column in a doc library but it must be done using a content type, I’ve written some instructions below on to get a document library setup with a rich text column:
- Configure ‘Advanced Settings’ for the document library and enable the management of content types.
- Create a new Site Column as multiline rich text.
- Create a new Content Type and add the column created in step 2.
- Add the Content Type to the document library using the ‘Add from existing site content types’ link.
- Save the document library as a template and delete the document library.
- Create the document library again using the template from step 5.
- Success! You should now be able to use a rich text column within a document library.
Hope this helps some people!