As Lightroom is based on non-destructive editing, you will never find a modified image in your Pictures folder.
Every edit on the file (crop, colours, levels, brushes, etc) is just a metadata, an instruction, written in the Catalog or in the XMP space, and it is reinterpreted each time to render the final picture.
This means that, if you want a physically cropped image to be imported in an external program, you have to make permanent rendition, so you have to export it to a new file.
For example, select the image, menu File -> Export, select the default Preset called "Burn Full-Sized JPEGs", then change Export to: to "Hard Drive", click Export, choose the folder where to put the new rendition.
You can also create a tailored export Preset that adapts to your needs (location, format, resizing, etc.)
Powerpoint could not insert the cropped image from the folder I created.So after following the instructions, I just copied the cropped image and pasted it into the Powerpoint. presentation. I hope this works.