Guide specifications should be in a digital format that is easy for for potential users to read and edit.

Microsoft Word is the word processor most widely used architects and engineers. But there is a compatibility issue between versions of Word. Word 2007 and more recent versions create files with the .docx extension; prior versions use the .doc extension. While it is easy to convert from one format to the other, a document can become discombobulated.

To find out which file format is most useful for guide specification, I posted a question on Linked In's Construction Specifications Institute (CSI) group. Within hours, I had my answer, demonstrating the power of social networks.

Theodore Smith, a specifer in New York City, wrote:

With Word 2007 and later you can use either .doc or .docx formats. The problems happen when you go backward from Word 2007 .docx format to earlier versions of Word .doc format files. If you are preparing guide specifications you should use the .doc format; there are a good number of firms and people who are looking at your guide specifications who are still using older versions of Word and .doc files and who will go elsewhere if your files give them problems due to incompatibility with their word processing programs.

This opinion was confirmed by other responses.

Several voices in the group also remind us that some specification writers prefer WordPerfect, a program that uses the .wpd extention. WordPerfect can open and convert .doc files.

RECOMMENDATION
If resources are unlimited, consider publishing your guide specification in multiple file formats for the convenience of users:

.html so it can be read in a browser.
.pdf so it can be readily printed without a word processor.
.doc for use in Word.
.wpd for WordPerfect fans.

In most instances, however, using the old Word .doc format will delight most, and be serviceable to the rest of, specifiers.