I have saved multiple images from google books. I wanted to convert them to a single pdf file, where in I need some inputs. The below two images(one png and one jpeg) are two continuous pages.

first page(png)

second page(jpeg)

I save them in my system. I converted them to pdf using the command below

convert books.png books.jpeg combined.pdf

However the combined.pdf is not giving me expected results, not the combination of the two.

I also tried making individual pdf files, then combining them using pdftk, with no luck

convert books.png book1.pdf

convert books.jpeg book2.pdf

pdftk book1.pdf book2.pdf cat output combined.pdf