Foxit PDF SDK for iOS

// Create a new document
FSPDFDoc* doc = [[FSPDFDoc alloc] init];

// Set a blank page width and height and add to document
floatw =612.0;floath =792.0;
FSPDFPage* page = [doc insertPage:index width:w height:h];

// Add note annotation
FSRectF* annot_rect = [[FSRectF alloc] initWithLeft1:10 bottom1:350 right1:50 top1:400];
FSNote* note = [[FSNote alloc] initWithAnnot:[page addAnnot:FSAnnotNote rect:annot_rect]];

// Set some properties for the annotation
[note setIconName:@"Comment"];
[note setSubject:@"Note"];
[note setTitle:@"Foxit SDK"];
[note setContent:@"Note annotation."];

// Reset Appearance
[note resetAppearanceStream];
NSLog(@"Add a note annotation.");

// Save PDF file
NSString* save_pdf_path = [output_directory stringByAppendingPathComponent:@"annotation.pdf"];
[doc saveAs:save_pdf_path save_flags