Most documents can be compressed using special computer algorithims so that they use less space on a hard drive.   This makes them faster to download over slow links such as a modem.   The most common compression format is zip.   Zip compressors and decompressors can be downloaded for free.   Even if you don't know what they are you still may have one installed already on your computer!   Try downloading one of the compressed archives and double click on it to seem if your computer already knows what to do with them.   If you are sure you don't have one here are two places you can download them from: