Well there can be many ways to do so. Since you haven't mentioned anything clearly about what sort of the PDF file do you have. but still I would like to answer in the best possible way. One of the reason of large size of the PDF file could be the sizes of the images inside the PDF file(Assuming that the PDF has images in the file). Convert the PDF file to DOC format. Then you need to have the the pictures extracted out of that converted DOC file. Change the format of these pictures to JPG or some other such formats that don't take too much of space. Put the pictures back into the DOC file. Convert it back to the PDF and its size will be reduced. There are other ways through some other softwares to just compress the PDF file and t ask you about how much size would you want it, at the time of conversion, but t does not compress it as much as manual methods can reduce the file size.
If you want to download this guide in PDF format, then use the links given below. The PDF file size is not the most important, but it's the fact that you can't simply extract the files. If you're looking for something a little easier, but you're still interested, then check out the How to Extract Videos from MP4 and MOVE files (How to Extract Videos from MP4 and MOVE files), if you're a Windows user then you'll also have to click on the link at this link. You'll have to click on the “Click Here To Download” at the top left, and you will have to save the files to your hard drive. If you're not a Windows user the steps you're required to follow will be in the same fashion. Download the program below, install it and open the extracted folder to see the results. Click here to Download. Extract YouTube.