Improve README documentation and error messaging.

README.md

@@ -18,6 +18,7 @@ FillablePDF is an extremely simple and lightweight utility that bridges iText an
     gem 'spring-watcher-listen'
     ```
 
+3. Read-only, write-protected or encrypted PDF files are currently not supported.
 
 ## Deployment with Heroku
 

lib/fillable-pdf.rb

@@ -21,7 +21,7 @@ def initialize(file_path)
       @pdf_form = ITEXT::PdfAcroForm.getAcroForm(@pdf_doc, true)
       @form_fields = @pdf_form.getFormFields
     rescue StandardError => e
-      raise "#{e.message} (input file may be corrupt, incompatible, or may not have any forms)"
+      raise "#{e.message} (Input file may be corrupt, incompatible, read-only, write-protected, encrypted, or may not have any form fields)" # rubocop:disable Layout/LineLength
     end
   end
 

lib/fillable-pdf/version.rb

@@ -1,3 +1,3 @@
 class FillablePDF
-  VERSION = '0.9.2'
+  VERSION = '0.9.3'
 end