Yes, it is possible.
In attachment section, use the "link" button, not the "file" button

Thank you for the quick response but I'm not getting it to work.

I click on the "Add hyperlink to file or webpage", enter the full file path name and file name and add a description, this adds an entry.

On the entry if I go along the entry options (left to right);

Hyperlink icon shows correct path and filename but if I click on it it does nothing.
The cross will delete the entry.
ID number
Wepage icon shows the correct path and filename but when I click on it I get 'preparing preview' and nothing happens.
Yellow icon with blue arrow shows the incorrect filename with missing characters, clicking on this does nothing.

Am I correct in thinking that clicking on the hyperlink icon should open the file in associated application?

I have tried this in both Edge and Chrome.

Thanks.

A bit further information which may help

The file location is recorded as file:///c:/users/anthony/desktop/temp.xlsx.
If I type is into the address bar in edge or chrome is does nothing, if I do the same with Firefox then it works as I would like (opens the file and I can edit it, save it and reuse the same link to open the updated file). However if I run Projeqtor in Firefox the hyper link button still doesn't work?

Thanks.

file:///c:/users/anthony/desktop/temp.xlsx is not an hyperlink it is location of a file.
You must use an url (starting with http or https)

Thanks for the reply but http and https are for web pages. I need to link to files on a network. These files are word and excel files. Is this possible ?

Thanks.

No, this is not possible.
Moreover, if you use file:///c:/users/anthony/desktop/temp.xlsx, it is a file on your desktop that other users won't see this "local" file