As Tom says PDFs are designed to represent precise positioning of content on a page. Content can be represented by that styled by fonts by vector objects such as boxes ellipses or free form curves or by bitmap frames. Many PDFs are abination of these content s. The size of a PDF depends on how it was processed. There are many allowedpression techniques in the PDF Specification. In addition when you make a PDF you can ask the PDF generator to reduce the resolution of your bitmap content in addition topressing it. A modern Word document (and PowerPoint and Excel) are ZIP archives that contain XML instructions that describe the document. These can often be quitepact especially if they do not contain fonts and if the graphic objects are external s. In a PDF all content must be including fonts and all bitmaps. So consider Tom Word doc that slightly larger than the PDF he made. I predict that with adjustments to the PDF export settings he could have made it much larger or much smaller. The answer is that it is always possible to make a PDF smaller when you export it if you know how to operate your PDF conversion tool. If you only have the PDF then you can likely make it smaller with Acrobat (FileSave asReduced File Size). As an example I started with a 781K Word doc and saved it as PDF from Word. The resulting PDF is 789KB and it was made using Microsoft PDF export tool. I then used Adobe Document Cloud PDF conversion on the same document and the PDF was 718K. Going back to the Microsoft generated PDF I used Acrobat Optimize function to reduce it to 572K. The size of your PDF is dependent on the content you put in plus your processing method.