"While Web documents and portable documents have distinguishing characteristics, the differences can also be viewed as situational and gradual rather than representing bright-line distinctions."
How about "The differences between the distinguishing characteristics of web documents and portable document can be viewed as situational and gradual rather than as representative of bright-line distinctions."
(Someone beat me over the head with a red marker about passive voice one. Not really. But they did instill the point about avoid the passive...)
"While Web documents and portable documents have distinguishing characteristics, the differences can also be viewed as situational and gradual rather than representing bright-line distinctions."
How about "The differences between the distinguishing characteristics of web documents and portable document can be viewed as situational and gradual rather than as representative of bright-line distinctions."
(Someone beat me over the head with a red marker about passive voice one. Not really. But they did instill the point about avoid the passive...)