Hi,
This would depend on how your PDF file is generated. If your PDF file is generated with our HTML to PDF converter, then there are no field in the result PDF file because the HTML to PDF converter only generates a visual rendering of the HTML page. It does not carry the interactive part over. If that's the case, then there is no way for you to check/uncheck the checkbox after it is generated. However it is possible for you to modify the input HTML to have the checkbox checked in your HTML, then render the HTML to render the checkbox as checked.
If the PDF file is generated through our PDF creator interface, or another PDF authoring tool that does generate interactive PDF form with checkbox field, then you can use code like this to check/uncheck the checkbox:
Code: C#
PdfDocument doc = new PdfDocument(pdf_file);
var field = doc.Fields[field_name];
field.Value = "1"; //Set to "1" to check it, "0" to uncheck it
Hope this helps. Please feel free to let us know if you still have any questions.
Thanks!