Is there a way to display and edit the contents of an Appian Document in the UI through webContentField component or by any other means?

Edit Document Properties Smart Service
a!editDocumentProperties(document, name, description, onSuccess, onError)

There is a smartservice available that has a corresponding SAIL friendly function you can use, unfortunately, it only lets you update the document's name & description (but not who created/uploaded it or when). Since you would be running it in SAIL, it may give non-admin users problems if they don't have the correct rights (since in a PM you can force the node to run as the process creator). You might have to pull the document's info and allow the name/description to be edited but not make the actual change until after the form is submitted.

I haven't figured out an easy way to change the "Created By" value. This probably isn't an issue for you, but a few times I found a need for this and couldn't readily do it.

You can get the document's info from the normal document() function or the smartserviec plugin: Content Details By UUID (6 functions in there including one by id#).

getcontentobjectdetailsbyid(228694)

Content Object [Name: capslock.jpg,
UUID: _a-0000e0bf-9911-8000-ac7a-680000680000_242115,
Parent: 22 Dispute Doc Folder, Parent Id: 228029,
Type: Document, Created by: rhartwic,
Created on: 2018-06-05 21:29:13.0,
Last updated by: rhartwic,
Last updated on: 2018-06-05 21:29:13.0,
Latest version: 1, State: Active Published,
Internal file name: accdocs3\178436\10069963.jpg]

I haven't found an obvious database table where Appian stores the document's metadata. If you found one you could try updating the data in the table, though there is a risk that this could cause corruption. The data may also be stored in the kdb files in which case you would have to only use the exposed/approved functions. Maybe Appian has some docs for manipulating the data via Java code.

Edit Document Properties Smart Service
a!editDocumentProperties(document, name, description, onSuccess, onError)

There is a smartservice available that has a corresponding SAIL friendly function you can use, unfortunately, it only lets you update the document's name & description (but not who created/uploaded it or when). Since you would be running it in SAIL, it may give non-admin users problems if they don't have the correct rights (since in a PM you can force the node to run as the process creator). You might have to pull the document's info and allow the name/description to be edited but not make the actual change until after the form is submitted.

I haven't figured out an easy way to change the "Created By" value. This probably isn't an issue for you, but a few times I found a need for this and couldn't readily do it.

You can get the document's info from the normal document() function or the smartserviec plugin: Content Details By UUID (6 functions in there including one by id#).

getcontentobjectdetailsbyid(228694)

Content Object [Name: capslock.jpg,
UUID: _a-0000e0bf-9911-8000-ac7a-680000680000_242115,
Parent: 22 Dispute Doc Folder, Parent Id: 228029,
Type: Document, Created by: rhartwic,
Created on: 2018-06-05 21:29:13.0,
Last updated by: rhartwic,
Last updated on: 2018-06-05 21:29:13.0,
Latest version: 1, State: Active Published,
Internal file name: accdocs3\178436\10069963.jpg]

I haven't found an obvious database table where Appian stores the document's metadata. If you found one you could try updating the data in the table, though there is a risk that this could cause corruption. The data may also be stored in the kdb files in which case you would have to only use the exposed/approved functions. Maybe Appian has some docs for manipulating the data via Java code.