Saving PDFs in MS Word - File size behaviour.

I've been using a Mac for years now and for many years when saving a word document as a pdf it would make a pdf with no discernible loss of quality and a file size almost the same size as the word document.  Easy.

Then several years ago using exactly the same procedure, the files sizes of the pdf became huge, often more than double, triple the size.  Compressing the pictures in the word doc to 'on screen', does help but it reduces the quality significantly and in most instances the file size of the pdf is still way bigger than than file size of the word doc.  The only way to fix it is to restart the Mac and then save the word doc as a pdf before you do anything else and it's saved as a comparable size. Great but it is still a pain having to restart and more often than not you need to compress the picture to 'on screen'.

I haven't worked out what exactly, but as soon as you do a bit of other work, and then save a word doc as a pdf, the file sizes become large again.  It's been an annoyance for years now and google searches don't seem to reveal any solutions or even anyone else with the same issue. I just end up on videos/websites that describe how to reduce the size of the pdf after it's been made, which is an extra step and ends up with a pdf where the pictures are low quality.

With every OS update I hope it's been fixed but after another update in the last couple months it's still the same.  It happens on multiple Macs but strangely the files sizes are bigger on Macs with bigger screens (16in MacBook Pro, 27 iMac).  Restarting those does get the file size down but it is still bigger than if saving on a 13 in MacBook Air so there obviously something at play at the OS level rather than just MS Word.  Having to restart and/or having to log into the Air just to make a pdf is very frustrating!  I know you can reduce the file size after but previously all you had to do was get the word doc to the size you wanted, usually by compressing picture to 'print quality' and then save as a pdf which would save at a similar size.

Any thoughts or ideas on why this no longer works would be gratefully received! I can't believe it's taken me this long to post this on here; it's been bugging me for years now!