How to get PDF form fields and values ?

[crocodile305]

when I would like to run formdata-extraction example ,I got an error like this.

Fatal error: Uncaught Error: Call to undefined method PdfToTextFormDefinition::ValidatePhpName() in E:\Xampp\PdfToText-master\PdfToText.phpclass:10873
Stack trace:
#0 E:\Xampp\PdfToText-master\PdfToText.phpclass(10519): PdfToTextFormFieldDefinition->__construct(Object(SimpleXMLElement))
#1 E:\Xampp\PdfToText-master\PdfToText.phpclass(10280): PdfToTextFormDefinition->__construct('W9', Object(SimpleXMLElement), Array)
#2 E:\Xampp\PdfToText-master\PdfToText.phpclass(2628): PdftoTextFormDefinitions->__construct('\xEF\xBB\xBF<?xml versio...', '<form checksum=...')
#3 E:\Xampp\PdfToText-master\examples\formdata-extraction\example.php(12): PdfToText->GetFormData('sample.xml')
#4 {main}
thrown in E:\Xampp\PdfToText-master\PdfToText.phpclass on line 10873

I would like to get PDF form fields and values.
Please tell me what is wrong and how to fix.
Thank you.