VBK files are proprietary VitalSource Bookshelf eBook files that typically use DRM (Digital Rights Management) to prevent unauthorized distribution. Because of this protection, they cannot be directly opened or converted by standard PDF tools.
If you are looking to convert your VBK file to a standard PDF, here is the breakdown of how to handle it. vbk file to pdf
.docx in Word, .xlsx in Excel, .jpg in Photos).Regarding "solid paper," if you mean converting a physical (solid) document to PDF, you can use mobile scanning tools. Google Help How to Convert VBK to PDF VBK files are proprietary VitalSource Bookshelf eBook files