So far answer for question is No, it is not possible.
From Internet found only that in DataDynamic(ActiveReports is/was a part of DataDynamics) reports is property
"append existing .pdf to report"
But ActiveReports is another product, which haven't this possibilities.
In my case we decide to use @Issam workaround(save .rdf file to another folder and use it later with another report).
I accepted own answer, only because the reason, question was created, was to check if this kind of possibility exists for ActiveReports