Keep in mind that the PDF format (ISO 32000) *is not* a word processing / page layout format. That means the editing we are familiar with in word processing / page layout applications is not supported.
You can perform minor edits. With Acrobat X the tool to use is the "Edit text" tool.
Using the word "edit" can lead to a false perception that word processor like editing is possible. Prior to Acrobat X the tool was (more appropriately so) named "TouchUp text" tool.
Regarding renderable text. If the PDF is created from some word processor or layout (or other application(s)) the PDF's textual content will be "renderable".
If a scanned image of textual content is brought into PDF there is no text present. There is just an image. OCR via Searchable Image or Searchable Image (Exact) will provide a 'layer' of hidden/invisible text (fonts are in rendering mode 3 - no fill, no stroke). Trying to "edit" this is really a waste of time (yeap, I've spent way too much time 'trying').
If ClearScan OCR is used the resultant output supports minor touchups.
You can even use the Touchup Text / Edit Text tool to select text and, via the Properties dialog, change to an installed font family).
With either ClearScan output or content that is rendeable text the save as / export to MS Word or RTF is support. Content can be edited in MS Word. A fresh, cleaned up PDF can be created. This approach is 'best practice'. Why? Well, much more than minor touchup will typically gobber the PDF (been there, got the t-shirt don't ya know).