My situation is like this: On my job, the old frameworks have to change and to save money they want a DIYS solution. I have a program found to make the plan but I do not want to start forming the beginning, the program can use the dxf file to import.
Question: I scan the old plans to jpeg / pdf, open with Inkscape, clean them up of unnecessary stuff and export them / save as dxf files.
Is it possible and will dxf file useable or have a restriction?

Hope someone can help me, I did not try it because it was faster when the community could speak instead of working on a program that was only short for one purpose.

What kind of restrictions are you asking about? Can you elaborate?

Inkscape works best for svg files. There is a huge number of versions of dxf files and I wouldn't use Inkscape for that. For dxf files, use Librecad instead - it's sort of open source variant to Autocad.

PDF can contain both raster (JPG, PNG, etc.) and vector (SVG, DXF, etc.) contents. (In case you didn't know.) If the PDFs you create will only contain raster contents, then Inkscape would not be the best choice, since Inkscape is a vector editor.

However, if the "old plans" are in a vector format already, there would be no reason to scan them to JPG. Likely Inkscape can import any vector format directly.