Merge branch 'stable' into develop

README.md

@@ -430,7 +430,7 @@ Both `vertical_strategy` and `horizontal_strategy` accept the following options:
 
 ## Extracting form values
 
-Sometimes PDF files can contain forms that include inputs that people can fill out and save. While values in form fields appear like other text in a PDF file, form data is handled differently. If you want the gory details, see page 671 of this [specification](https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdf_reference_archive/pdf_reference_1-7.pdf).
+Sometimes PDF files can contain forms that include inputs that people can fill out and save. While values in form fields appear like other text in a PDF file, form data is handled differently. If you want the gory details, see page 671 of this [specification](https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.7old.pdf).
 
 `pdfplumber` doesn't have an interface for working with form data, but you can access it using `pdfplumber`'s wrappers around `pdfminer`.