Portable Document format (PDF) is the most widely used format for storing and transferring data. The large size of these files can hinder its storage and transfer. So compressing PDF is the only possible way to make this a user friendly format. Compression is the process of reducing the file size, helping the transmission of data. Compressing PDF mainly refers to image compression.
PDF uses different compression algorithms. Some of them are:
JPEG and JPEG2000
The different compression algorithms can be mainly classified as lossy and lossless compression. Lossless compression doesn't alter the quality of the content in a file. The lossless algorithms are CCITT compression, ZIP, LZW compression ,Flate compression and RLE compression. The lossy algorithms have higher compression ratio than lossless, but detection in the quality of the content can be observed. JPEG and JPEG2000 is a lossy algorithm.
PDF compression can be done by making use of a few techniques. Using vector graphics for images, reduces the size by a considerable amount. Compressing vector image data using ZIP compression can also be done for compressing PDF. Compression will minimize the fonts in the documents and reduce the number of embedded fonts that use a lot of file space. Flatten flat forms by using the option Advanced -> PDF optimizer -> Discard objects. This will compress PDF by merging the form with the page. Convert the PDF to grayscale if colors are not required. Insert high quality images in the PDF. Prepare the image for maximum compressibility before inserting them in the file.One of the very common methods of compressing PDF is choosing File->Save As option. Saving the file and overwriting the existing file will remove the unused elements in the file. This will also help in compressing PDF file size.
There are a few Acrobat plug-ins that can be used to compress data. Acrobat Distiller can be used to compress all the images first, before recompressing them for a PDF. Compressing PDF can increase your storage space and save time.