As a tutor or class member you may often need to create Word or PowerPoint files, typically using many images and scaling them down within the application. It may not be realised that the full image scale/resolution is still retained in the file even though it now appears smaller, and this means that the file can often be quite large. It is better to scale the image size first, using an image manipulation tool such as IrfanView or Paint, but this can be tedious.
If the document is being used in a presentation, whether in the classroom or online via Zoom, etc., file size doesn't matter, but often the presentation needs to be sent to class members or others. This is typically done by saving as a PDF, which will also have full-scale images. Most email clients will object if attachments are larger than about 20MB so this can present a problem. Equally, a large PDF stored on a website means significant download bandwidth for the end user. In these days of mobile devices, excessive bandwidth usage can be a costly. If you have an Acrobat Pro subscription or alternative, PDFs can be compressed significantly, but those products are expensive.
One solution is to upload large files to cloud storage and provide a link. This solves the email problem, but not the download size. A better way is to use existing image compression facilities within the original application, the existence of which is not widely known. Here is how it's done on Windows (Apple Mac has slightly different options):
In Word or PowerPoint, select Save as PDF. The screen then shows a More Options link:
Click on More Options. The next screen shows some options at the bottom. One is Optimize for Minimum Size, which works well.
Another way is to use the Tools dropdown, which offers:
Selecting Compress Pictures allows you to choose the degree of image compression:
Selecting E-mail or Web will typically reduce the size of the resulting PDF (if it uses many images) to a fraction of what its size would otherwise be, e.g. down to less than 10% of original size. Visual inspection of the resultant PDF typically shows no obvious difference in appearance, and the file can then be emailed or placed on a website without issues.
PDF Conversion Online
If all you have is a large PDF and don't have access to the original document, Adobe offers online tools which provide many of the features of Acrobat Pro for free, including image compression:
https://www.adobe.com/acrobat/online/
(There may be limits to how often this tool can be used).