As the image, from the scan, is just that - an image. It has not "fonts".
If OCR'd, then the hidden (invisible) text will use whatever Adobe assigned as the default font type for text rendering mode 3 (Acrobat 8 or 9) for OCR modes Searchable and Searchable (Exact image). You could try, on a test page, to select this text and see if the default font attributes can be changed.
With Acrobat 8, OCR with Formatted Text & Graphics provides an OCR layer that replaces the image. Again, using a test page, you could select this replacement text and try changing font attributes.
With Acrobat 9, OCR with ClearScan provides OCR text that uses a specific Adobe font type for ClearScan. Once again, with a test page, select the text output of ClearScan. You should be able to change to a different font type (provided the font is (a) available to Acrobat from the system and (b) the font has no license restrictions that preclude embedding it into PDF. With a different font type in use, perhaps its size can be changed.
Also with Acrobat 9 Professional Extended (most likely with Acrobat 9 Professional as well).
Preflight Fixups - Embed fonts (even if text is invisible). If a PDF uses fonts which are not embedded into the PDF file they are embedded. This fixup embeds fonts even if they are only used for text which is invisible (text rendering mode 3). It is required that the respective fonts are present in the system's font folders. Some fonts may have a flag indication that their license does not allow embedding. In this case the fonts are not embedded into the PDF.
You could try the above. Once the invisible/hidden OCR text is embedded you could try selecting text and changing font attributes.
If OCR'd, then the hidden (invisible) text will use whatever Adobe assigned as the default font type for
text rendering mode 3 (Acrobat 8 or 9) for OCR modes Searchable and Searchable (Exact image).
You could try, on a test page, to select this text and see if the default font attributes can be changed.
With Acrobat 8, OCR with Formatted Text & Graphics provides an OCR layer that replaces the image.
Again, using a test page, you could select this replacement text and try changing font attributes.
With Acrobat 9, OCR with ClearScan provides OCR text that uses a specific Adobe font type for ClearScan.
Once again, with a test page, select the text output of ClearScan. You should be able to change to a different
font type (provided the font is (a) available to Acrobat from the system and (b) the font has no
license restrictions that preclude embedding it into PDF. With a different font type in use, perhaps its size can be changed.
Also with Acrobat 9 Professional Extended (most likely with Acrobat 9 Professional as well).
Preflight Fixups - Embed fonts (even if text is invisible).
If a PDF uses fonts which are not embedded into the PDF file they are embedded.
This fixup embeds fonts even if they are only used for text which is invisible (text rendering mode 3).
It is required that the respective fonts are present in the system's font folders.
Some fonts may have a flag indication that their license does not allow embedding.
In this case the fonts are not embedded into the PDF.
You could try the above. Once the invisible/hidden OCR text is embedded you could try selecting text and changing font attributes.
Be well...
Be well...