Preview corrupts PDF when using Save As from Mail attachment

Nigel__Cro wrote:

From Preview I 'Save as' to a location in My Documents.

Don't do that.

I open the saved copy in Preview and there is corruption throughout the file.

PDF is not what people think it is. Apple only supports a very limited, much older subset of PDF. If you create new PDFs on a Mac, they will be fine to send out. But if you receive PDFs from outside, always save the original (using a copy operation in the Finder), and ideally, lock it to prevent modifications. Apple's Preview will modify practically everything it touches, especially if you do a "save as" operation. So don't ever, ever do that.

Preview is obviously making changes to the file as it saves it.

Yes. Absolutely.

These changes are corrupting the original file.

Yes. Absolutely. Been happening for many years. Widely reported and common knowledge.

What is going on?

Any ideas??

Seems like you've already worked that out. Apple Preview is corrupting your PDF. Don't use it to open PDF files that you didn't create. Always make a copy of the original in case you forget.

Adobe created the PDF standard, originally, so I expect that use of the free Adobe Acrobat Reader might be a more robust approach. There are a number of PDF files I have received over the years (not many, but a few), that Preview does not open properly or save properly. There are many options for PDF files in terms of custom content and I don't think Preview can handle all of them. For instance, some forms fill fine with Preview but others do not. Also, with pasted in graphics, sometimes Preview does not show the content properly. I consider Preview to be a mostly usable but reduced capability PDF program.

I have never encountered problems with Adobe Acrobat (either the full version or the free Reader) or with PDF Expert, which is a paid utility that has many options for modifying PDF content, and also has a built in OCR capability for PDF files.

I have done this multiple times, and have never had Preview corrupt a file.

Two tests you may want to do to circumscribe the issue:

1 - try doing a similar procedure but instead of opening the attachment in Preview, select another application that can open pdf files (Safari, or Skim, or TeXShop, for example). Save the file. Same problem?

2 - do the same thing, but with a different pdf; for example, send a known good pdf to yourself by e-mail, and then open the attachment in Preview, and save. Does it have the same problem?

My suspicion is that this pdf is subtly incorrectly formatted, and that this reveals itself when trying to save.

Try printing the pdf but hitting the "save as pdf" button at the bottom of the print dialog instead of hitting the print button.

CheviotView wrote:

Is there an alternative to Preview which does not corrupt a PDF created by another program?

There are alternatives, but they're not very good. The downside of free software is that, regardless of the volume of complaints, people do tend to stick to the freebies and ignore anything else. That really dries up the market for alternatives. And sometimes the cure is worse than the disease.

It's usually better to just identify problems and work around them. For the problem you describe, you can make copies of original documents or lock the original documents to prevent corruption.

You can always use Adobe's PDF tools. Sometimes I use Master PDF Editor for PDFs that Apple Preview isn't able to open. There are other options if your only concern is corruption of PDF documents. In many cases, people are complaining that Apple Preview can't even read a particular PDF. Most 3rd party PDF tools still use Apple's underlying OS-level PDF support libraries. They might better handle the problem with corruption that you describe, but they won't help with other PDF problems. Adobe and Master PDF Editor have completely separate PDF engines, so they are more robust alternatives.

Nigel__Cro wrote:

Thanks Guys,

I have a number of ways of getting a 'clean' PDF. What I am really interested in is, what is Preview doing during the process of writing to disc that is causing the corruption? It is happy to render the file accurately direct from the email, but is it doing something in the background to facilitate the render that then means it changes the file that it writes?

I would like to know that too, but I have no idea.

It would be difficult to know even if we had the file, or a similar example where corruption crops in. As it is, without any information about the file, it is downright impossible to know.

I deal with pdf files every day, and have been doing so for decades now, and I don't recall a file getting corrupted by Preview before. I suppose it would take having the file in the hands of someone with deep knowledge about the internals of the pdf format, and the time and drive to pore over it. Alas, I don't have that knowledge.

How did your friend create the pdf?

Is there an alternative to Preview which does not corrupt a PDF created by another program?