I have many books scanned to PDF (the content are the graphic images, no OCR processing). Will Kindle Classic be able to view such PDFs? Aren't they too heavy? Acrobat Reader on my old smartphone crashes when trying to open them.
The kindle device is generally able to open PDF containing pages scanned to graphic images.
My Kindle Classic generally loads them without any problem, but if they are scanned to too high resolution or contain high resolution graphics, it crashes, so such heavy PDFs will be an issue. Maybe newest devices, such as Kindle Paperwhite, having more processing power, will handle them better.
Note also that 2-pages scans will be very high to read. On Kindle Classic you can display them as fit-to-page, which may be impossible/too hard to read, or you can use zoom, which is very uncomfortable to work with.
So I'd answer, yes, as long you have single-page scans scanned to moderate resolution.