A project package is a single file in which a CAT tool bundles a translation job's bilingual files, resources and instructions, so the translator can open the job in one step and send the finished work back in a matching return package.
The project manager creates the package from a project in their CAT tool and decides what goes in. Typically that is:
A Trados package is a zip file with its own extension, so you can unzip it to see what it holds.
The workflow has two halves. The translator receives the package, works on it, and sends back a return package with the finished files. The project manager opens it and their project is updated. In Trados, the return package holds only the translated files, without memories or termbases.
Trados creates a return package only for files that arrived in a project package. memoQ imports Trados packages and exports .sdlrpx return packages; other tools may open a package but not produce a return package the sender's tool accepts. Our post on how to open an SDLPPX without Trados compares the options.
An agency sends you manual_de-DE.sdlppx. Inside are three SDLXLIFF files, a project translation memory and a termbase. Before accepting, you drop the package into a word count tool and see 6,200 words, 1,400 of them repetitions. You translate the files in memoQ, which imported the package, and export manual_de-DE.sdlrpx. The agency opens it in Trados, the translated files replace the empty ones, and they generate the final German manual.
TraduQ's free tools help with packages in the browser: the word count and quote tool reads an .sdlppx directly, the SDLTM converter opens a Trados memory found inside, and the QA checker checks SDLXLIFF, MQXLIFF and MQXLZ files before you deliver.