Adobe Community: Message List - Form XObjects without Resources - do we ignore ancestor forms?

Re: Form XObjects without Resources - do we ignore ancestor forms?

forums_noreply@adobe.com — Sat, 25 Oct 2014 07:47:10 GMT

Yes, that's what prompted this question. We use a fairly popular PDF library to reorder and combine documents from various files. The original Page becomes a Form and the Resources inheritance ends up like my question. It doesn't attempt to add the 'missing' Resources to fix it up (can't really blame them).

Re: Form XObjects without Resources - do we ignore ancestor forms?

forums_noreply@adobe.com — Sat, 25 Oct 2014 00:50:21 GMT

Me too. I should also note that many utilities will not respect inheritance from page object if they do certain transformations such as convert a page to a form XObject (e.g. for placing as a graphic). I just point this out in case, in future, anyone reading this sees a shortcut and is tempted.

Re: Form XObjects without Resources - do we ignore ancestor forms?

forums_noreply@adobe.com — Sat, 25 Oct 2014 00:43:16 GMT

Yes I'll agree with that, what I really meant is we shouldn't be surprised if we get errors. I work a lot with printers and generally I'm happier if a printer just fails and gives me a chance to fix the file myself, rather than guessing what to do.

Re: Form XObjects without Resources - do we ignore ancestor forms?

forums_noreply@adobe.com — Sat, 25 Oct 2014 00:15:37 GMT

I take issue with "We should therefore get a missing font error as the PDF is invalid". If a PDF is invalid (as it would be) the behaviour is undefined. Unless you are using software that claims to be a complete PDF validator, the PDF reader may take any behaviour and would be correct, including

- an error

- a default font

- missing text

- looking at the chain of form XObjects

A PDF creator should of course only make correct PDFs rather than rely on accidental or deliberate permissiveness in any particular viewer.

Re: Form XObjects without Resources - do we ignore ancestor forms?

forums_noreply@adobe.com — Fri, 24 Oct 2014 23:55:18 GMT

Thanks for that. The PDF that prompted this query was version 1.3, so I thought it would be best to refer to that version of the spec. Does the ISO spec relate to all versions or just the later ones?

I'll see if we can get access to it, I don't currently have a copy.

Re: Form XObjects without Resources - do we ignore ancestor forms?

forums_noreply@adobe.com — Fri, 24 Oct 2014 14:22:59 GMT

First – the version of the PDF spec you are using is VERY OLD. You should be using the international standard – ISO 32000-1:2008 as it is the official document at this time.

Second – the topic you raise has come up many times on the ISO committee and how to clean up and clarify that section. You will find the version in 32000 much clearer and more specific on how to handle it. Which is that if there is no Resources dictionary at all – then you inherit. If there is a Resources dictionary, then regardless of whether it has fonts (in your case), you do not inherit.

Form XObjects without Resources - do we ignore ancestor forms?

forums_noreply@adobe.com — Fri, 24 Oct 2014 04:00:39 GMT

Hi, I'm just wondering what happens in the below situation.

We have a Page which includes a form XObject #1, which itself contains another form XObject #2.
Form #2 uses a font but has no Resources dictionary. The font is defined against the Resources dictionary of form #1 instead.

Based on the PDF spec (which I've copied below) a client application should refer to the original Page object to see if the font is defined there but should not check form #1. We should therefore get a missing font error as the PDF is invalid. Is this correct?

For reference the PDF spec v1.4 says the below.

"A form XObject or a Type 3 font’s glyph description may omit the Resources entry, in which case resources will be looked up in the Resources entry of the page on which the form or font is used. This practice is not recommended."