I do these things with
http://freepdfxp.de/.
Normally it is used to print to PDF, but it is fairly easy to define a new printer, change the output format to PNG (or JPG,...) and you get a numbered list of files (one per page of the original file).
I use it to create PNGs from PDFs which are protected regarding copy&paste. I then do OCR on the PNGs and still can access the text. Therefore I use a resolution of 600 dpi.
This is not completely what has been asked for (single jpg or bitmap) but once you have all the PNGs the rest is a question of finding a software that can join these into one big bitmap.
Stupid idea: Create a web-page of all the PNGs, open it in firefox and make a screenshot via Screengrab extension into one big file.
The crashing may be due to the huge size of the resulting bitmap. This way you have different steps to proceed and try (and not crash) each individually.
I have created PNGs from large PDFs so I think this wouldn't crash. I have no idea what Screengrab will behave like.
tg227f102(at)sneakemail.com