Refer to Acrobat X Standard's online Help.
It describes what Acrobat X Standard can do and the tools available within Standard.
For Editing PDFs start here:
The discussion on editing text and objects begins here:
What is all to often overlooked/ignored is the statement on the "Choosing a tool" page.
"A common misconception about PDF documents is that they should behave like any other document that contains images and text, letting you freely move or edit items on a page. A PDF is like a snapshot of your original document. You can perform minor touch-ups, but if your PDF requires substantial revision, it’s easier to make changes to the source document and regenerate the PDF."
It cannot be stated strongly enough that only *minor* changes to small text strings on the PDF page are supported.
PDF is not designed to support "editing" of content, layout, or format such as one is used to when using a word processor or page layout application.
What PDF "is" can be ascertained from a close read if the ISO standard for PDF (ISO 32000).
Consequently Acrobat (or other apps for that matter) only support *minor* edits.
Your client will be able to use the Edit Text tool available with Acrobat X Standard.
This tool lets one perform *minor* edits to text strings.
Expect to do this to a few words at a time and at best a complete line.
The tool's capabilities are *not* comparable to what one is used to in a word processor.
Even when doing *minor* edits it is best to save often and even save as to a new file name.
It is all too easy to goober the PDF page content (and the PDF).
Best Practice for a success path is to always perform content, format, layout edits in the source authoring file. Then output a new PDF for collection of Comment/Markup annotations via a Shared Review.
With either FrameMaker or MS Word one can do "round trips" of Comments between the a single, master authoring file and the output PDF.
However, this requires the use of Acrobat X Pro.