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Last Week on My Mac: Problems of PDF

The Eclectic Light Company:

I was asked why some PDFs would only display properly when opened in Adobe Acrobat, not in Preview or any other third-party PDF viewer on a Mac. Surely PDF is a standard, so why can only one vendor’s products handle those documents properly?

The answer to that question is, as you might expect, not a one-liner. But it brings with it some important lessons about open standards and the internals of macOS. There isn’t any snappy summary, so please bear with me.

Suffice to say, the PDF specification was already huge when Adobe submitted it to become an International Standard, and that has since ballooned further as new use cases were added.

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What is more worrying is that PDF formats aren’t designed to be robust in the face of file corruption. It’s not difficult to change a few bytes in a regular or PDF/A document and make it totally unusable.

History tells us that crucial records, here the text of the oldest epic to have been committed to writing, often get damaged, in this case over a period of around four millenia. In the mere quarter century that PDF has been around, countless users have suffered file corruption and errors which have made it impossible to open their damaged PDF files.

I've had recent experience of PDF files becoming corrupted and unreadable. Thankfully, they weren't of great value, but this underlines the importance of having a regular backup system in place to make sure all your important data is retrievable, preferable from more than one place.

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