Adobe InDesign natively supports the export of its own documents to PDF format, so it should be the natural choice for INDB to PDF conversion. Other option would be to find some kind of InDesign viewer and use the Print function to save the document as PDF instead printing on paper.
Convert Adobe InDesign publication to Adobe Portable document format.
We found 2 software records in the database related to .indb to .pdf file format conversion.
Microsoft Windows software - convert indb to pdf on Windows
Professional desktop document publishing software from Adobe
Convert from indb file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned indb to pdf. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Apple macOS / Mac OS X software - convert indb to pdf on OS X
Mac version od Adobe's popular document designing and publishing software