[gs-devel] Can Ghostscript stream PDF?

David Newall ghostscript at davidnewall.com
Wed Jun 2 00:42:35 UTC 2021

On 2/6/21 6:10 am, Till Kamppeter wrote:
> So I want to know now, if I start Ghostscript and feed in a PDF file, 
> would Ghostscript output each page of it as soon as the data of the 
> page has completely arrived or would Ghostscript read in the full PDF 
> before it starts rendering it? 

PDF files contain a cross-reference table, normally the second last part 
of the file, without which the file cannot be usefully used.  The 
location of the cross-reference table is specified in the trailer, i.e. 
the last part of the file.  This means that in general, a PDF file must 
be read in entirety before any useful processing can commence.

See PDF 32000-1:2008 Document management -- Portable document format -- 
Part 1: PDF 1.7 section 7.5 for details. 

Some PDFs have a copy of the trailer and the cross-reference table just 
after the header to permit processing the file sooner but you cannot 
rely on that, and, as a trailer must always be at the end, the 
possibility exists that the copy after the header might be wrong.  As 
explained in the prior-mentioned specifications, PDF files "may be 
modified by later updates, whichappend additional elements to the end of 
the file".

In other words, in general, yes, Ghostscript must read the full PDF 
before it starts rendering it and that is true for any program that 
processes PDFs.

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