pdftk utf8 pdf form fields

[nirdshabo]

Added support for UTF8 fields which has been missing from the wrappers to pdftk but do exist on the framework

[smarquez1]

+1

[jkraemer]

I chose not to add new *_utf8 methods but instead added a :utf8_fields option that triggers usage of dump_data_fields_utf8. Could somebody possibly provide a sample pdf with non-ascii field names for use in test cases?

[smarquez1]

Thanks for your work. I created this pdf sample with Master PDF Editor. The last field has a UTF-8 name. Hope it's useful
#15