Primary sources can either be first-hand observation/analysis, or accounts contemporary with the events described.
Primary sources document events, people, viewpoints of the time.
When research is more era, rather than event driven, scope of possible primary sources broadens considerably.
Primary sources represent one person's perspective; frequently will be used with secondary/tertiary sources to broaden the lens through which a researcher is looking at an event, era, or phenomenon.
It is important when using anything as a primary source that the researcher be cognizant of and sensitive to the bias of the observer/analyzer that created the primary source, and also to the broader cultural biases of the era in which the primary source was created.
The researcher's perspective, or the arguments or points for which a researcher plans to use a primary source as evidence, is significant in determining what sources will be primary.
Reproductions of primary sources remain primary for many research purposes.
Some attributes are based more on the perspective represented in the source and context in which the source is being used by researcher.