One of the solutions which I will be showing here is to compress the pictures in the file. Open your document and click on one of the pictures. A picture toolbar will appear. If there is no picture toolbar, click on the top menu -' view' -'Toolbars' -'Picture', as shown on the image below. Then click on the icon to compress the pictures. 
After you had click on the icon to compress the picture, a pop-up box like the one below will appear: 
Select 'all pictures in document' and 'web/screen' then click on OK. A pop-up box will appear again - just click 'Apply".
After you had click on the icon to compress the picture, a pop-up box like the one below will appear: Select 'all pictures in document' and 'web/screen' then click on OK. A pop-up box will appear again - just click 'Apply". 
Save your file again, maybe under another name and you will be able to see the difference in the size of the files before and after the pictures are compressed.
