Pdf size increase after importing

This is a PDF file I found online:

And after I import this file to DT3 and add some highlights, the file size is just doubled.

Have you used search here in the forum? PDF size, for example, gets me numerous hits. The lowdown is that PDFKit is likely to be the culprit (you can test that by annotating the same PDF in Preview and seeing whether the file size increases then too), and there is nothing you can do about it (other than use a PDF editor which doesn’t use PDFKit).


Thank you for the reply! I searched for this problem but I am not patient to read it though. Sorry about that. Thank you anyway!