Open PDFs, Edit Them, Save Them?

Pages cannot, and because of the way PDFs are inherently structured, very few applications can do this, and most of them do not do so satisfactorily (at least, not for major editing of text).

What you can do is to open the pdf in preview, copy the text, paste into a pages document, and then make another pdf from the pages file, but this is, obviously, a cumbersome and kludgy workaround.

As far as I know, it is only the Pro version of Acrobat that will allow you to edit PDFs, and even then it is not set up for changing large chunks of text where elements on the page should reflow.

PDF is not a format that is intended for editing or composing. If you need to update a piece of information in a PDF file, it is almost always easier to go back to the original format (Pages, InDesign, Illustrator, QuarkXPress, etc.), do the edits there, and then re-generate the PDF. This avoids tons of hassles.

I don't know what is your purpose with PDF documents related to Pages, but :
- You can open PDF documents produced by Pages with Preview and insert comments or «post-it» yellow styled comments. You can also make red circles to signal what has to be changed and so on. Once it's done, save your PDF modified in Preview, and send it for collaborative work. Beware, all you comments cannot be edited afterwards.
Now, back to Pages: if you want to use it in a collaborative way, add Comments. Select something on the page of the Pages document, Menu Insert>Comment. Then send your Pages document (for example zipped) to your buddy equipped with Pages.

iMac G5 PPC 2,1 Ghz Mac OS X (10.4.9)

«post-it» yellow styled comments

They don't have to be yellow. If you want to use Preview to fill a form with a white background for instance, create a comment, open the color picker with the comment active and choose the color you want (like white). The background will change to the color you select.

Ha ha, thanks for the tip Barbara, Post-it are (still) yellow in my mind and in the default options, even if now they can possibly display more flavours (smiles).

iMac G5 PPC 2,1 Ghz Mac OS X (10.4.9)