Win32 communicating with ASP.NET

We currently have a desktop application that we'd like to move to the web, almost completely.

The problem is, that in order for that to work, we need to figure out a way to transfer files, detected in folder(s) using a simple desktop application, upload them to the web, and attach them to the users current 'session'.

Our client will create a 'New page', fill in details, transfer files from a 3rd party software, and these files needs to be attached to this page.

The files then need to be rendered/shown in an image container directly on the 'New Page' (we'll do that by showing a file-type icon).

The important thing is that, the files doesn't attach themselves to the wrong page.

The "easy" way of doing this, could be to add another field to the user database called "CurrentPageId", that is updated when a client clicks 'Create New Page' or enters the specific page and cleared when the user clicks 'Save Page' or leaves the page.

Workflow

• User creates a 'New Page' on our website, fills in some information
• The user then export files from a 3rd party software, our Win32 application detects them and uploads them to a WEB API
• The files should then attach themselves to the users current page and display itself on that page

The problem I'm seeing is, how do we clear the 'CurrentPageId' if the user leaves the page, crashes, closes the browser and so on. It's a big no no if files attaches themselves to the wrong page (a user can have thousands of pages).

We cannot have the user select the files on the website and upload them, because the files depending on the 3rd party software they are using, save files in folders with tens of thousands of files, naming convention can be anything from dates, to unique identifiers and so on, and the user can be anything between 20 and 75 yrs old.

Does anyone have any experience with a desktop application communicating with an web application like this? Any pointers or ideas would be grateful