It seems that the Dolphin EasyConverter is the only program capable of exporting .dec files to PDF format which pretty much defines and limits the options for this dec to pdf conversion. As far as known this is the only way how you could accomplish this conversion.
Convert Dolphin EasyConverter project to Adobe Portable document format.
We found one software available in the database for this conversion.
Microsoft Windows software - convert dec to pdf on Windows
A file conversion software
Convert from dec file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.