Attachments
Any kind of file can be attached to a note. In Markdown, links to these files are represented as a simple ID to the attachment, clicking on this link will open the file in the default application. In the case of audio, video and pdf files, these will be displayed inline with the note and so can be viewed or played within Joplin.
In the desktop application, files can be attached either by clicking the "Attach file" icon in the editor or via drag and drop. If you prefer to create a link to a local file instead, hold the ALT key while performing the drag and drop operation. You can also copy and paste images directly in the editor via Ctrl+V.
Resources that are not attached to any note will be automatically deleted in accordance to the Note History settings.
Important: Resources larger than 10 MB are not currently supported on mobile. They will crash the application when synchronising so it is recommended not to attach such resources at the moment. The issue is being looked at.
Downloading attachments
The way the attachments are downloaded during synchronisation can be customised in the Configuration screen, under "Attachment download behaviour". The default option ("Always") is to download all the attachments, all the time, so that the data is available even when the device is offline. There is also the option to download the attachments manually (option "Manual"), by clicking on it, or automatically (Option "Auto"), in which case the attachments are downloaded only when a note is opened. These options should help saving disk space and network bandwidth, especially on mobile.
Opening attachments
In the note viewer, clicking an attachment link opens that attachment.
In the rich text editor, ctrl+click opens that attachment.
In both cases, the attachment is opened in the default editor for that file type. The editor can generally be customised in system settings.
Unknown file type warning
Opening some types of attachments can be dangerous. Some computers try to run some attachment types as programs. This means that opening attachments from an untrusted source could allow someone to steal information from your computer or worse.
When is it safe to open an unknown file type? If you created the file, attached it to a Joplin note, and haven't shared the note with anyone, it should be safe to open. Otherwise, avoid opening the attachment, especially if you don't recognise the file type.
If you're certain that a file type is always safe to open, regardless of its source, check the Always open this file type without asking box to stop receiving warnings for that file type. It might make sense to do this, for example, if you work with a large number of .doc files and know that they're safe to open in the version of Word you have installed.
What are some examples of unsafe file types? This depends on your computer. For example, on most Windows systems, .COM, .EXE, and .BAT files are unsafe.