PDF documents are content rich, as they hold text, different fonts and graphics and make the presentations more interesting and easy to understand. However these elements also make the file size huge which makes it painful to store or send them online. A compressed version can save storage space and takes less time to be attached with emails. Compression here means reduction in the file size. This also makes it less time-consuming for the email recipient to download the attachment.
Content compression can be done by removing all extra space characters, using a single repeat character in place of a string of repeat characters and replacing frequently occurring characters with smaller bit strings.
PDF files already come with some compression functionality built in, as they are designed to be loaded with graphics and other space consuming stuff. Compression techniques used on PDF can be either lossy (some information is lost in the compression process) or lossless (all the content can be restored on decompression). Lossy algorithms like JPEG compression can be used to shrink image and audio files, but they are not useful for text and program files since some information is lost in the compression process. For text and program files one needs to reduce the file size with the help of lossless compression algorithms where all the data can be restored on decompression.
To downsize a PDF file to the utmost one should insert the bitmap images in such a way that the dimensions are minimized. The user should also look out for the best quality images and use black and white images wherever possible. RGB color space is better for compression than CMYK. When color is not needed one could use grayscale. Additionally thumbnails should be turned off since vector based graphics usually work better than bitmap graphics. Also one should avoid using too many fonts because each additional font takes 40k in getting embedded.
Compressed PDFs help to reduce file size while maintaining the quality of the original software. Some compression software can also remove text annotations, page labels, bookmarks etc.