PDF documents are content rich, as they hold text, different fonts and graphics and make presentations more interesting and easy to understand. However these elements also make the file size huge. A compressed version can save storage space and takes less time to be attached with and downloaded from emails. Compression here means reduction in the file/data size.
PDF formats are usually designed to compress information as much as possible. 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.
A PDF compressor reduces the file size by condensing image, text and graphics. It removes unused elements, metadata, bookmarks, thumbnails, comments from the document. Compressor feature includes optional encryption of PDF content. A PDF compressor makes a very compact, fast web view file which can be easily transferred and occupies less storage space. It has the ability to process entire folders of PDF files.
To compress 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 the file size while maintaining the quality of the original software. Some compression software can also remove text annotations, page labels, bookmarks etc. Some packages also have special graphic interfaces.