Windows Explorer has a search function which can filter found files, based on some attribute or other – so you return files that are only of a particular type or age, or maybe of a specific size. The problem is, the understanding of what is a big file has changed over the years.
In the days of the floppy disk, any file larger than 1Mb was a bit unwieldy. When server hard disks cost £1,000 per Gb, then file servers would impose quotas of maybe a few 10s of Mbs per user.
But now, with storage so cheap (e.g. a 4Tb hard drive is a little over £100, Azure storage is a few pennies per Gb/month, and OneDrive seemingly can’t wait to give it away) it’s easy to become blasé about very large files.
One particular culprit in the generation of unnecessarily mahoosive files is PowerPoint. With the ease of inserting graphics and video, especially, it’s not hard to get files well into double figures of megabytes, which can be problematic to email and take ages to open. There are a few tips that can help you keep the size a little more trim.
Delete stuff you don’t need
Well, duh. Obviously, deleting stuff can make a big difference to the file size: before distributing a deck, maybe dump the hidden slides and the many appendix slides unless you feel they might be a useful reference…
It’s sometimes not as easy as ditching slides you don’t need, however – the template you’re using might have a lot of imagery that’s unnecessary in it, so it may be worth cleaning up a little.
Go into the View tab, look under Slide Master and you’ll be able to see the slide templates that define the look and the layout of new slides. It’s not uncommon to find hundreds of these, though in most cases they’re not a cause for concern – unless they have lots of images embedded.
This is particularly the case when an elaborate slide deck is produced for a conference, and people start using that template as the basis for their own presentations, because it’s got a really nice background or whatever – not realizing that the template might have 10Mb of grinning stooges holding long-obsolete mobile devices and conference logos from years gone by. If you don’t use the graphics slides, feel free to delete them from the master, then Close Master View to go back the regular deck. (Might be an idea to save a copy of the deck first, just in case you muck it up…)
Look within
The PPTX file format that has been used by PowerPoint since 2007 is part of the Open XML file formats – the idea being that instead of a proprietary binary file, the artefacts and contents within the file are described using XML according to a published format, so other applications could re-use the files. In order to achieve this and not end up with huge file bloat (XML not being well known for its brevity), the whole shebang is compressed.
What you may not know is that all of the Open XML formats use the same compression as ZIP files, and if you rename the .PPTX extension to .ZIP, you’ll be able to see inside it.
Navigate to your file location, and make sure can see the file extensions – go to the View tab in Explorer and tick the File name extensions box if you can’t see them. Make a copy of the PPTX file you want to work on, select it and right-click to Rename (or just press F2). Now overtype the .pptx bit at the end with .zip, and agree to the dire warning that the Earth might stop turning if you continue.
Now open the ZIP file up and look in a couple of places to see what is likely to be making it huge – ppt\media and ppt\embeddings are a couple of notable sources (the 
former when you’ve maybe got a video or just lots of high-res pictures embedded, and the latter is a common source of embedded XLS files which might be unnecessary… ie. Maybe you could get away with a simple copy of relevant data, rather than the whole file?). Maybe the best way to slim down the file is to open the un-renamed one in PowerPoint, then navigate to the place where the huge content was and resize, compress or replace it.
Compress pictures
A very simple way of cutting the size of large files without digging around in their innards might 
be just to compress pictures – you can get to that from the Format tab when you have a picture selected, and 
individually reduce the size and resolution of each image.
Alternatively, when it’s time to save your work, use Save As and under the Tools drop down in the lower right of the dialog, you can invoke the same function, but which applies 
to every image in the deck.
Choose the appropriate resolution – Screen is probably a good one for PPT, though the same picture compression functionality is also available in Word and Outlook, so if you’re pasting images into an email then resizing them, it’s an idea to compress them and you can get away with an even lower resolution there.
