This blog post will cover how to generate the preview of pdf files using Carrierwave gem. Carrierwave gem has an inbuilt " manipulate! " method which reads the file and loops over every page. This " manipulate! " method works as expected for a pdf having 300-400 pages but when I uploaded a pdf having 1000+ pages my machine crashed!!! That is when I started debugging the code and found out that there is an issue with the manipulate method. Here is my original code. class MyUploader < CarrierWave :: Uploader :: Base include CarrierWave :: RMagick def cover manipulate ! do | frame , index | frame if index . zero ? # take only the first page of the file end end version : preview do process : cover process : resize_to_fit => [ 310 , 438 ] process : convert => : jpg def full_filename ( for_file = model . source . file ) super . chomp ( File . extname ( super )) + '.jpg'