If you want to generate a document then edit it before sending it or downloading it there are a few options:
First thing to consider is if you want to edit it in Google Docs which is great because its all cloud based and the field remains current with every edit and you can easily collaborate with other coworkers. This would be our recommended process. The other option is to just download the file in Word, then open it in word, and work with it from Word to save as a PDF manually.
You should configure your Document Action to generate the Google Doc only and not output to PDF. Configure it to save the google doc URL to a text field that you should create on your object (see this article for more information on how to create this URL field). Create the button to say something like “Generate Document” since this button/action is all about just generating the google doc, not sending it.
Once you have the google doc URL saved in the field, then without anything else you could easily just click the link in that field from the page layout which will open the doc in google docs. Then you can edit it from there. When finished just close it because all changes made are saved in real time on google docs. And the link to that google doc always remains and always current.
Optionally you could add a formula field or visual force section to embed the google doc directly into your page layout so you can always and immediately see the google doc and edit it right from Salesforce. See this article if would like to learn how to embed the google doc into your page layout.
A good solution is also to provide an if statement to only show this section IF there is a google doc URL populated in your field. You would just use standard embed code and reference the google doc URL to embed from that URL. See this article for an example formula of that gets the google doc id out of the full URL.
To send the completed document you have some options:
If you are planning to email the document, you can merge the google doc URL field into a link in your email template to send a link to the google doc.
Or you can create a formula field that can create a URL to link to the google doc but will export to PDF upon clicking it. See this article for more information on this option.