Hm, once a person use a "unwanted" word like PDF in the same time he ask a question with topic calibre and conversion, helping people maybe oversee the real question (he ask for EPUB to PDF). But maybe I am wrong. If so, please apology.
I sometimes do this kind of conversions for presentations too and I hadn't ever that problem. (And sometimes a travel guide works much better as PDF than as EPUB
)
@liwei, It's not a good idea, to blame a program without talking about what you are doing with a real example. That's why you get such a harsh answer. Better way is to explain exactly what you had done, what parameters you choose for the conversion and a little example so that people are able to check out the problem. That's much better as going into this kind of conversation...
To maybe push you a little in the right direction, please take a look on two things. One is the page setup section in the conversion dialog. calibre will take account to the chosen reader profile to recalculate picture sizes and page sizes if you don't make correct entries for PDF-Output. That is as well my second hint. Please take a look to the details. Especially to the check box for override paper size set in output profile with correct paper size you need and preserve aspect ratio of cover if you have as well a issue with this.
Most of my conversion going the right way with setting up paper size I need for a presentation.
If this all will not do what you want make first a conversion to DOCX, make your adjustments you need and do then a conversion to PDF.
Best regards,
DD