The honest answer separates the format question, which is solvable, from the rights question, which sets the real boundary, so both clearly:

The rights boundary first, because it governs everything: most Kindle books are sold with DRM, digital rights management, that ties them to your Kindle account and devices and that DRM exists specifically to prevent format conversion and copying. Removing DRM to convert a book generally violates the terms you agreed to and, in many places, the law, regardless of it being your purchased book. So the legitimate scope is genuinely limited, and this forum will point at what is permitted rather than how to strip DRM.

What is legitimately possible: DRM free content converts freely. Books and documents you own without DRM, many independent titles, your own documents sent to Kindle, public domain works, convert to PDF with Calibre, the same ebook tool that handles EPUB, which reads the Kindle formats and outputs PDF cleanly. Personal documents you sent to your Kindle are yours to convert without issue.

The legitimate routes for DRM content you want in another form: Amazon's own ecosystem often has the answer, the Kindle app runs on many platforms already, possibly including the device you wanted PDF for, removing the need to convert and some content offers different formats through your Amazon account. For printing, some Kindle content permits limited printing through the Kindle apps directly. Checking what Amazon actually permits for your specific books often finds a legitimate path to your real goal, reading elsewhere or printing, without conversion.

The principle worth stating: the goal is usually reading on another device or printing, and the legitimate solutions address those goals directly, the Kindle app on the target device, permitted printing, DRM free purchases where the format matters to you, rather than converting DRM protected files, which is where the legitimate boundary sits. For DRM free material Calibre does exactly what you want, and matching your actual need to what is permitted usually finds a clean answer.