Seeding

Micro-Seeders seek out planets that have a chance of supporting life and dust them with a mélange of bacteria cysts, spores of yeast and fungi, moss and ferns, aquatic and aerial plankton, plant seeds and all sorts of other hardy biota. Which take hold varies widely, as much by chance as by suitability, but this does push most suitable planets onto the carbon - chlorophyll path. This is why the vast majority of life in the mundane universes has compatible DNA.

Later, a Macro-Seeder may come by and transplant an array of standard life forms; it's up to them to compete and see which survive to evolve. How standard or unusual they become depends on local evolutionary pressures and how much time they have. Whether sapient races, are seeded - and whether they survive - is separate factor. When this happens, the line is crossed from Seeding to Colonization.

Some worlds develop life totally on their own. Such may have a different DNA-analog, or merely incompatible amino acids. Most Seeding projects are designed to pass by such auto-vivified worlds.
Similarly, worlds with Indigenous populations are also generally left to evolve on their own, whether these Indies evolved independently or are descended from some earlier colonization project.

The Seeders of the Ancients that remain today are generally automated, elusive, and quite able to defend themselves. Their varied deigns demonstrates that they were developed independently by several Ancient civilizations. As most operate beyond range of Imperial science expeditions, The Imperial Ministry of Archaeology has captured only a few for study. A few others are being observed by dedicated task forces, sometimes actually "camping" within the Seeder ship.
These devices of the Ancients, grand though they may be, are suspect, for they are often incorporate Artificial Intelligence. Most such AI remain dedicated to their original programming, but AI always carries the risk of accident giving rise to consciousness. Such self-aware synthetics are at risk of developing a hostility to their organic predecessors and so must be destroyed.

The Imperial Seeding Mission

"Organic intelligence must defend itself against the Synthetic."
So states The Credo, the raison d'etre of the Empire. The First Corollary of The Credo is "Spread Organic Life." This makes Seeding The First Virtue.
(SEE The Organic Credo)

The Seeding is a moral imperative, the material benefits of which are secondary. That is can serve as a procurer to later colonization, a similarly meritorious activity, which both spreads organic life and Raises worlds, is a very nice benefit.
(SEE Colonization)

The Imperial Ministry of the Sacred Mission of the Seeding (IMSMS, or Imisamise, pronounced "i-mee-sa-MEE-see") includes co-opting or rendering assistance to Ancients' Seeders, launching new Imperial seeding expeditions, and encouraging subject and client states and megacorps to conduct Seeding expeditions of their own.
Much of this is done with surprisingly low levels of technology.
As subjects and clients (whether states or megacorps) are generally more interested in areas that they can reasonably hope to colonize in their shorter-sighted investment views, it remains to the Imperial expeditions, whether governmental or through benevolent intuitions, to promulgate seeding expeditions further afield.
It is often convenient for Imperial Seeding expeditions to double as scouting forays into areas that the Empire expects to eventually bring into The Harmony.

Rendering thousands of worlds more fit for colonization is a major, if officially secondary, benefit of the Seeding campaign. The worlds thus benefited, as well as those states and megacorps investing in them, are, naturally, taxed to support further Seeding. Such taxes may be in cash or in kind, which latter may be used to support Seeding and / or colonization activities in areas less likely to be able to pay their own way.
Whether the inhabitants of a world realize that their existence is result of Seeding or colonization expedition is irrelevant; ignorance does not absolve debts or mortgages, material or moral. Indy (indigenous) populations may suffer a negative reaction upon realizing that their world is actually owned by someone else, that they are in debt, and that a portion of their world has already been allotted to colonization by an extra-stellar investor.
Happily for the Imperial Seeder Campaign, this is a matter for the Ministry of Colonial Affairs bureaucracy to deal with.