This article shows how to search a string in whole pdf file:

With this method you can use a PDFDoc instance to search in whole pdf file and store/manage results.

- (void)customSearch:(PDFDoc *)doc ofString:(NSString *)string
{
    BOOL caseSensitive = NO;
    BOOL wholeWord = NO;
    for (int i = 0; i < doc.pageCount; i++) {
        // get page
        PDFPage *page = [doc page:i];
        [page objsStart];        

        // find in page
        PDFFinder *finder = [page find:string :caseSensitive :wholeWord];                

        // manage each search term contained in this page
        for (int c = 0; c < finder.count; c++) {
            // start position
            int firstCharPos = [finder objsIndex:c];
            NSLog(@"page: %i", i);
            NSLog(@"pos: %i", firstCharPos);
            // do custom actions
        }
    }
}