Hi @LEVAF. I am definitely not an expert in this area, but I will share a few things that may lead you in the right direction. Images can be resized and I think that it should affect the export, but I can’t verify that right now and am honestly forgetting. Regardless, here is a quote from the Obsidian Help about that syntax:
You can resize images using the following syntax:
For markdown images, use 
For embeds, use ![[image.png|100x100]]
To have the image scale according to its aspect ratio, omit the height ![[image.png|100]]
A cleverly created find and replace can automate adapting all of your image embeds in one swoop.
There is also a way to force page breaks at locations by adding some code where you want the content immediately after to be started on a new page in the PDF export. Here is a link to that technique. It may help you in certain cases: Page Breaks for PDFs - #2 by ottovanluchene
What you are experiencing has also been my experience, and I believe that there are likely additional things that could help us. I should also mention that you can adjust the scaling percentage when exporting PDFs.
If the reason you are exporting to PDF is to get the functionality of interaction provided by PDFs like zooming, etc, there is a world of css customization that creates many useful adaptations to the note preview/edit viewing experience.
Good luck! Thanks.