Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
I am not quite sure that I get the picture, of what is happening with your HP Officejet's top feeder or document feeder.
1. it never feeds the original document through all the way, but stops
2. it doesn't state that there's a 'document jam'
3. you can still photocopy a single sheet laid face-down on the glass sheet
then if all those 3 are true, you may have a defective paper presence sensor switch in the top feeder. That means the paper feeds in some, but stops when it is not sensed (which strictly ought to result in a 'document jam' message, so maybe only (1) and (3) are required for this diagnosis.)
The printer would need servicing in that case, unless some error message is involved, and unless you can find/clean/unjam the paper presence sensor switch in the printer.
Please elucidate how the problem is behaving. Also let me know whether you are considering replacing the HP printer in question rather than repairing it. In either case, I could help you further.