imageUrl
The image URL or image virtual path to which to add its page(s) as thumbnail(s). Each page will be added as a new thumbnail.
firstPage
The 1-based index of the first page to load.
lastPage
The 1-based index of the last page to load. Must be greater than or equal to firstPage. You can pass -1 to load from firstPage to the last page in the file.
thumbIndex
The 0-based index at which the new thumbnail element(s) should be inserted.
text
The thumbnail item text.
This example replaces the first thumbnail with a "image1.jpg" and set the thumbnail text.