Problem: "Damaged" file

Error message: "There was an error processing a page. The document may be damaged."

Likely cause: Old version of Acrobat Reader

Slides and other handout materials for CIS 422 are in PDF (portable document format) version 2, which requires Acrobat Reader or Acrobat Exchange version 3. The Reader is available for several platforms (Solaris Sparc and x86, Linux, Mac OS, Windows 3.1, 95 and NT, HPUX, etc.) free from Adobe, http://www.adobe.com.

The most common problem is attempting to read PDF version 2 documents with a PDF version 1 viewer, e.g., an older version of the Acrobat Reader. The older version of Reader will give a bogus report of a corrupted file. (Software engineering question: What should Adobe have done in the first place to prevent this? For a hint, see how versioning is handled in Internet standards like MIME, PNG, etc. [Answer] )

If you try to view a PDF document with Netscape, and it reports an error in the file, there is a good chance that the Netscape PDF plugin is an old version (Acrobat version 2 or 1). You can get the newest plugin from Adobe. Here is a tip from Chris Schleicher on configuring Netscape, in a reply to a student:

>When I select [a document from a Winter term class] 
>I get a window saying Acrobat Reader 2.1 and then an error window with the
>message
>	There was an error processing a page. The document
>may be damaged (9).

Netscape doesn't necessarily use the same version as the one in
your path.  Here it's using the old version.  To fix this, go into
Netscape Edit | Preferences | Navigator | Applications and find the
association for PDF files.  Change the application from
    /local/apps/AcroRead/bin/acroread %s
to
    /local/bin/acroread %s
to make Netscape do the right thing.

Problem: Funny characters, bad spacing, bad fonts

You see funny symbols in the page, or if the fonts look awful or the spacing is bad (e.g., lines extend beyond the edge of the page or labels extend beyond boxes).

Probable cause: Missing fonts or bad font substitution

PDF files can contain "embedded" fonts (the font files are included in the PDF document itself), or substitute special "multiple-master" fonts, or it can use whatever fonts are available on your computer. Embedded fonts can make the PDF file very large and slow to download, so I avoid them. Usually, the fonts you see will not be exactly the same as the fonts I actually used, but they will be close enough that the slide is quite readable.

There are a variety of ways in which font management can go haywire.

• Encoding errors: If there are only a few weird characters scattered about the slides, these are probably special punctuation characters that are encoded in different ways on different platforms. This probably isn't a problem in the PDF per se, but in the original document file that I used to produce it. I use Microsoft PowerPoint to prepare slides, and while PowerPoint is claimed to be completely compatible between Windows and Macintosh versions, in fact it frequently screws up character encodings when I move files between platforms. (I use desktop Macs but my laptop runs Windows and Linux.) If the encoding problems make it difficult to understand my slides, the best option is probably to ask me to regenerate them.
• Spacing problems: Poorly spaced words (particularly, gaps between letters in a word) are usually a result of using fonts that have the same name but which are not really the same. Sometimes this also happens when I move presentations between Mac and Windows machines, but sometimes it happens when your computer substitutes a font for the font that I used in the slides. In particular, if you have a font called "foo" and I have a font called "foo", but they are not really the same font, you're likely to see very poor character spacing. This happens mostly with very common fonts like Times. You can get some idea of what is going on by opening the File|Information|Fonts dialog in Acrobat Reader.
• Missing dingbat fonts: Acrobat usually does a good job of substituting "multiple master" fonts for fonts that I don't embed in the document. For example, when I use Tekton (a sans-serif font designed to resemble hand-lettering on architecture diagrams), what you will probably see on the screen is "Adobe Sans MM" which will look pretty much like Helvetica or Arial. This strategy doesn't work at all for so-called "dingbat" fonts such as Zapf Dingbats (equivalent to Monotype Sorts) or Symbol. Acrobat assumes everyone has those two standard dingbat fonts, so that it doesn't need to substitute for them, but there are gobs of other dingbat fonts for everything from map symbols (Carta) to postal bar codes (USPS) to pictures of various food items (Mini Pics Little Edibles). Acrobat does not use font substitution for dingbat fonts. If I use any of these, I will normally embed them in the PDF file so that they will display correctly on your screen. If somehow I don't manage to embed them correctly, you are likely to receive an error message stating that certain characters cannot be displayed.

If font management problems make slides unreadable, please try first to get some idea of the nature of the error. Sometimes the File>>Information>>Fonts dialog of Acrobat Reader will help. Then write me an email describing the problem as precisely as possible. I will then check the PDF file and possibly fix it.

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Answer to question, "What should Adobe have done to prevent this error:"

As I will repeat again and again this semester, software changes. You must anticipate change and prepare for it. When Adobe designed the first version of PDF and the Adobe Acrobat software, they could only guess at some of the ways the standard would change in the future, but they must have known that the standard would evolve over time. So, what should they have done about it?

A simple solution is to include a version indicator as part of every document, in a form that can remain stable in future versions of the standard. For example, every MIME-encoded email message contains a mail header indicating the current version of the MIME standard. So far the only version is 1.0, but it is very likely that someday there will be a version 1.1 or a version 2.0. When that happens, well-designed email readers that conform to version 1.0 will not report corrupted files when they receive a message encoded with the newer version of the standard. They will be able to recognize that the message is in a newer version of MIME, and notify the user that a newer version of the software will be required to decode it. Of course, including this information in the document does not guarantee that all software will make proper use of it. I don't know whether Adobe omitted versioning information from the PDF format (unlikely, since it is based on PostScript, and PostScript does include versioning information albeit only in the form of an optional comment), or whether (as is more likely) the information is there but the proper version checking and reporting functionality was omitted from the Acrobat software.

Last update: 2 January 1999
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