It's a set of basic tips (make sure you have a recent version of Acrobat, add meta-data, divide large files, etc.), but one important one is:
Step #2. Identify the text
You cannot manipulate the text in an image like text in a word processor. To do that in Acrobat, you need to open your image-based PDF and run “optical character recognition.” Go to the “document” menu. It will scan your document and translate the image-text into text that can be edited so search engines can read it.
Acrobat may not have been able to recognize all of your PDF’s text after running OCR, however, so some portions may be marked “suspect.” To find your PDF’s suspects and check their accuracy, click:
Document > OCR Text Recognition > Find all OCR Suspects
This will enclose all suspect words in boxes and allow you to check whether the translation is correct or whether it needs to be modified.
Now go out there and spam the world with those optimized PDFs!