Unable to complete half filled Form.

Hi, Can anybody help please,

I am completing a Fillable PDF form from the Countryside Stewardship,

I had 99% completed the form, inserted my signiture, but wasnt sure of one piece of information -

Saved the file,

Found the information out,

Went to open the pdf today,

but cannot make any amendments to anything I have filled in or tick the box I need to!!

I can select 'fill and Sign' and select a box but only get Bong Bong Bong if I type!!

Please help before I go completly mad!!

Tom