Converting a bunch of pdf files to pnm without loosing resolution

[Paul Smith]

On 8/25/07, Andy Green <andy at warmcat.com> wrote:
> >>> Is there any way of converting a bunch of pdf files to pnm without
> >>> loosing resolution?
> >> What happens when you use the -dpi= option on pstopnm?
> >
> > OK, Andy, but how can one find out the dpi's of our pdf file?
>
> Well the pdf is not normally already rasterized in the case of text, so
> for that there is no "dpi of our pdf file".  It will render the text
> nicely according to the dpi you asked for.
>
> If there are raster images (at various dpi) in the pdf then it will
> scale them to the dpi you asked for AIUI.  So I guess you should pick a
> dpi that is close to the highest image dpi in the pdfs (eg, 300) and run
> with it.

Thanks, Andy. In fact, the pdf file that I have got contains a scanned
document. Is there some way of determining the dpi used in the
scanning work?

Paul