I went to www.guruji.com. Generated a Gujarati string "Guruji". I copied it to clipboard.
Next, I went to Microsoft Word 2007 and pasted that string into a document. Also, I pasted that string in Find in Microsoft Word. I could find the string. I also selected the string and copied it to clipboard. I got the same string.
Next, I generated two PDF fiies using Microsoft Word's own PDF generator and other with doPDF 7.1. I do not have access to Acrobat.
I could not search the Gujarati text in both files though it looked the same as in Microsoft Word.
When I copied the text from the PDF files to clipboard I got garbage.
I suspect that PDF generators may be a problem. But I am not sure.
As a side comment, Adobe Reader search text-box cuts bottom pixel row from Gujarati 'u's. FoxIt does not.