There are some PDF structures that the Kindle's PDF engine doesn't support and that lack of support can result in this symptom.
I encountered one such PDF, a download from Archive.org, in which almost all pages displayed blank on my K3 with only a few images displaying. None of the text displayed. I "fixed" the PDF by opening it in Adobe Reader on my WindowsXP PC and printing it to a PDF virtual printer driver to create a new simpler PDF.
The printer driver I used in
PrimoPDF, available free. There are a number of similar apps available. These install as a printer allowing any application that can print to create a PDF file. If you use MacOS you'll find a similar function built into the OS.