show do
attributes_table do
attachment_row("My doc", :attachment, label: 'Download pdf file', truncate: false)
end
end

index do
attachment_column :document
end

truncate
: you can pass truncate
attribute to toggle truncating the filename. attachment_column
truncates by default.
label
: if you want to show another text instead of the filename.
It can be a string, or a proc if you need another attribute from the model
attachment_column "Who wrote it", :pdf_file, label: proc { |book| book.author.name }