Hi Matthew

NOT via the REST API but the path to file looks like this

http://localhost/crm/eware.dll/do/Gatecom+Inc/Panoply+Customer+Letter190570093.pdf?SID=108347163661659&Act=1282&Mode=0&FileName=Gatecom+Inc\Panoply+Customer+Letter190570093.pdf

The library/documents entity can be accessed via the REST API.  That would give you much of the information you need to assemble the path.

Trying to do this on an external URL with something similar to below, but it fails to work. I'm guessing I need some kind of SID. 

crm.CustomerDomain.ie/crm/eware.dll/do/AN+Other/Example.jpg?FileName=AN+Other\Example.jpg

Is there somewhere I could direct their IT guys to go to for more information. I have pointed them to the help.sagecrm.com area but doesn't seem to be anything in the guides there about downloading files out of CRM, just how to create the Library entry when uploading.

Have a look at this article:  (+) Sage CRM 2022 R1: REST improvements (Quickfind) - Sage CRM Hints, Tips and Tricks - Sage CRM - Sage City Community

That explains how the some of the REST calls need a SID.  The Postman collection for Sage CRM available via developer.sage.com explain how a SOAP call needs to be used first to get a SID.

Once you have the SID you can build the link to fetch the file. 

Is there somewhere else I need to post on this subject to get help. The customer's developers have some back with the following

"...We can't receive the image through the feed currently because we have no path URL from the API to link the image to the feed. We were trying to fix this manually by combining the folder plus file name using a SID number, but this throws a 404 error. 

 We need help, with an example if possible, to set this up correctly via the API feed..."

Hi Matthew

The API is not designed to serve an image or file.  BUT this idea of building a path to a file does work

http://localhost/crm/eware.dll/do/Gatecom+Inc/Panoply+Sales+Quote601158125.pdf?SID=166740267048548&Act=1282&Mode=0&FileName=Gatecom+Inc\Panoply+Sales+Quote601158125.pdf

http(s)://[servername]/[installname]/eware.dll/do/[folder name]/[filename]?SID=[ValidSIDvalue]&Act=1282&Mode=0&FileName=[folder name]\[filename]

The full path is needed and if it is built correctly then the next error I would expect is  

"Authentication required, Browser session mismatch. "

1. Open Sage CRM  > Administration > System > System Behaviour 
2. Ensure "use browser session security" is disabled

Customer now has this working. Thanks everyone who replied.