This is the Premiere Elements VIDEO editing forum... a PDF is not a video file... what program are you using?
If you wish to use pictures from inside a PDF file, the only way I know is to use Acrobat to open the file and do a "save as" to save to a JPG file
Definitely the pdf is not a supported format in Premiere Elements.
I have not tried the following approaches first hand but I have seen them mentioned online for pdf to video file.
1. Google search will bring up PDF to Video Converters where the resulting video file can have a MPEG, AVI, or WMV format. The important matter here, if you intend to bring the MPEG, AVI, or WMV into a Premiere Elements project, is properties of this converted file, especially the video and audio compression involved in the converted file.
2. There was one suggestion to use a screen capturing program to record your pdf file opened on the computer and one that you are scrolling through. Here again the properties of the output file needs to be considered for Premiere Elements compatibility.
We will be watching for your progress.