Secure Portable Document Dilemma

We need a way to create secure legal documents in which most of the document is locked, but some fields are editable. These documents are for distribution to our partners, who need the ability to edit the open fields and save their changes. Unfortunately Adobe Acrobat is not a good solution for us. It would be too costly for our partners to purchase licenses for their entire sales teams. Has anyone else had a similar problem? Are there affordable applications similar to Acrobat which are secure and still produce a widely accepted file format? Any help at all would be greatly appreciated!