Is it possible to use a file that is stored on my local computer in an Integromat scenario?
This is not possible. You can use one of the supported cloud storage services such as Dropbox or Google Drive to upload the file manually, and then use the corresponding Integromat app (Dropbox, Google Drive...) to download the file into your scenario.
If you already have a file URL, it is also possible to use it directly with a general HTTP module called "Get a file".