What does "importing" a file actually mean?

Does opening a file always imply that a file is imported?

Generally speaking, each program stores its data in its own format. This means that, besides saving data which can generally be used, it can also save attributes specific to this data.

The same applies with IsoDraw. Besides storing pure geometrical data, e.g. the start and end points of a line, other additional information which is important for IsoDraw is also stored. This not only includes such things as the attributes of an element, e.g. pen, style or shadow, but also data which is only relevant for IsoDraw, e.g. the depth of a thread. Since the "Thread" element does not exist in this form in any other program, IsoDraw must write its own format in order to be able to recognize this element as a thread again later.

When IsoDraw opens one of its files in the way described above, no import procedure takes place. The information contained in the file is available in the exact form required by IsoDraw.

The situation is different when you open a file from another program, e.g. Adobe Illustrator. The same applies, of course, to this program as for IsoDraw, i.e. it stores its data in accordance with its own structure. Adobe Illustrator does not use ellipses or threads as elements, but Bézier paths instead. Consequently, an Illustrator file only contains information about Bézier paths which Adobe Illustrator is naturally able to read with ease.