Term Search in Adobe Acrobat Reader

Hi, 

I am using Acrobat Reader to search terms in monthly periodicals that have been scanned into pdfs. This is part of a larger project, and there are multiple people using Reader to search the same terms in the same pdfs. I am consistently coming up short of the number of terms that my search generates. My Reader is not detecting all terms. I have tested this, I will type in, for example, the word "arms." I will see it highlight one or two occurances of the word, but miss others. Is this a problem there is a solution to?

Thank you, 

Mary