I have tried to use Calibre, but it said DRM prevented the process. Are there any other converters which can do this? If there is one that can help, please tell as soon as possible. I need it now.
Yes, as you said the epub books are DRM protected then the Calibre does not work at all.
If you want to achieve converting, you can refer to this:
I believe this is helpful.
You computer must be authorized to handle such documents before you can actually remove DRM protection from a file. First you need to download Adobe Digital Editions. Download and install this application and create an Adobe ID. Log-in with the Adobe ID you have just created and authorize the computer then you can use any DRM removal application and I can assure you that will work. You have been receiving the error because your computer was not authorized to perform such operations.
There are two tools that you can have a try to convert DRM ePub to PDF.
1.Epubor Ultimate Converter (Shareware)
Calibre can't convert the DRM-ed ePub to other formats. It works with non-DRM ebooks only. If your ePub books are got from Apple's iBooks Store, I'd suggest you try TunesKit iBook Copy. It's a smart iBook software that can easily reomve DRM protection from iBooks ePub without losing any info. After that, you can use some other tools like Calibre to convert the DRM-free ePub to PDF. For more details, this guide will help: https://www.tuneskit.com/ibook-tips/how-to-convert-epub-to-pdf.html.