Notebooks on OneDrive increase in size after I delete OneNote pages

Hello,

I have 1 TB of storage on OneDrive  but I am nervous that even this space wont be enough to store all my Notebooks on cloud. This is due to one particular fact that I have noticed recently. 

I inserted a PDF as printout on OneNote page. This pdf was around 82 mb. At this stage the size of my Notebook was 342 Mb. After I deleted that page, I noticed that the Notebook size became 1.02 Gb. I am not able to figure out what is taking up the space on OneDrive?

Please Help.