@Willi – also fixed width spaces will not help here.
The PDF Readers tend to have a "smart" algorithm to convert whitespace into a single blank character, if you copy the text to the clipboard. Or, if the distance is wide enough, convert it to a tab. You can see this with Apple's Preview app. Some pdf viewers even insert a paragraph sign to the copied contents for the whitespace. Like Firefox' own pdf viewer. But only sometimes!
Depends on how the text is composed and if whole lines or whole paragraphs are selected. If it can be read as part of a paragraph or as part of a list. Or other criteria we cannot know…
Here a test with some text selected in Firefox' own pdf viewer copied to the clipboard:
Note: All text selected.
Then copy/paste it to TextEdit on to InDesign.
Did the same with Chrome browser, Preview app on OSX, Adobe Reader XI.
Here the results:
Different "smart" algorithms at play here…
The results would be different, if only some parts of the text are selected and copied.
Uwe