Usually whoever sends you this type of PDF would create it as an able to be signed document so there could be the basic problem of who made the file... Or, if you just downloaded a form thinking you could sign and date it....that is a problem, since you cannot do that with Reader.

Adobe documents are protected- but perhaps the sender made a mistake.....
I suggest that if you were sent it you ask the sender if they realized the document is not usable to you and see what they say. You should have gotten some instructions about how to add your signature....
You may just have not noticed a message when you opened the .pdf file....

I don't think we are able to give you much help with this, since it could involve document security and we do not assist with working around this type of thing, though there certainly are solutions to the problem we don't do it here.

 

Thank you so much for this valuable information.I tried to go to edit which didn't work.I have so much to learn.I ask alot of questions.But that's the only way to find good answers.I will try what you say the next time I get a PDF File to sigh.
Gene Hammond