This client script will attach files from the items by types to the current document.

AttachItemFiles.js

function GetFileAttachments(frm, arrItemCode) { 
    //Get files which are added to given items
    frappe.db.get_list("File", {
        filters: [
                ['attached_to_name', 'in', arrItemCode],
                ['attached_to_doctype', '=', "Item"]
            ],
    		fields: ["file_name", "file_url", "folder"],
    		limit: 9999
    	}).then((data) => {
    	    let arrFileExt = [];//File extensions
    	    let arrFileExtInfo = [];//json
    	    let strFileExt = "";
    	    let jsonFileInfo = {
    	        file_ext: [],
    	        file_count: []
    	    }
    	    let dIndex = -1;//File index search
    	    for(let i=0; i<data.length; i++) {
    	        strFileExt = data[i].file_name.substring(data[i].file_name.lastIndexOf(".")+1);
    	        if(arrFileExt.indexOf(strFileExt) === -1) {
    	            arrFileExt.push(strFileExt);
    	            arrFileExtInfo.push({'file_ext': strFileExt});
    	            jsonFileInfo.file_ext.push(strFileExt);
    	            jsonFileInfo.file_count.push(1);
    	        } else {
    	            dIndex = jsonFileInfo.file_ext.indexOf(strFileExt);
    	            jsonFileInfo.file_count[dIndex] = jsonFileInfo.file_count[dIndex] + 1;
    	        }
    	    }
    	    for(let i=0; i<arrFileExtInfo.length; i++) {
    	        strFileExt = arrFileExtInfo[i].file_ext;
    	        dIndex = jsonFileInfo.file_ext.indexOf(strFileExt);
    	        arrFileExtInfo[i].file_count = jsonFileInfo.file_count[dIndex];
    	    }
    	    
            const fields = [
            {
                label: 'Files',
                fieldtype: 'Table',
                fieldname: 'files',
                description: __('Select File Types'),
                fields: [
                {
                    fieldtype: 'Data',
                    fieldname: 'file_ext',
                    options: '',
                    reqd: 0,
                    readonly: 1,
                    label: __('File Type'),
                    in_list_view: 1
                },
                {
                    fieldtype: 'Int',
                    fieldname: 'file_count',
                    options: '',
                    reqd: 0,
                    readonly: 1,
                    label: __('File Count'),
                    in_list_view: 1
                }
            	],
                data: arrFileExtInfo,
                get_data: () => {
                    return r.message//ERR
                }
            }]
            var d = new frappe.ui.Dialog({
                title: __('Select File Types'),
                fields: fields,
                primary_action: function(dataTable) {
                    let arrPromFile = [];
                    for(let i=0; i<d.fields_dict.files.df.data.length; i++) {//Her dosya turu icin
                        strFileExt = d.fields_dict.files.df.data[i].file_ext;
                        //Does the file type is selected?
                        if (typeof d.fields_dict.files.df.data[i].__checked !== 'undefined') {
                            if (d.fields_dict.files.df.data[i].__checked === 1) {
                                //Select the files which have the same extension
                                for(let j=0; j<data.length; j++) {//For each file
                                    if (strFileExt == data[j].file_name.substring(data[j].file_name.lastIndexOf(".")+1)) {
                                        //Extensions match
                                        const docFile = frappe.model.get_new_doc('File');
                                        docFile.file_name = data[j].file_name;
                                        docFile.attached_to_doctype = frm.doctype;
                                        docFile.attached_to_name = frm.docname;
                                        docFile.file_url = data[j].file_url;
                                        docFile.folder = data[j].folder;
                                        arrPromFile.push(frappe.db.insert(docFile));
                                    }
                                }
                            }
                        }
                    }//File operations are completed.
                    d.hide();
                    Promise.all(arrPromFile).then((result) => {
                        frm.reload_doc();
                    })
            	},
            	primary_action_label: __('Attach Files')
            });
            d.show();
	    });
}

frappe.ui.form.on('Request for Quotation', {
	refresh(frm) {
	    frm.add_custom_button(__('Get Item Attachments'), function(){
                let arrItemCode = [];
            
                $.each(frm.doc.items,  function(i,  d) {
                    arrItemCode.push(d.item_code);
                });
                GetFileAttachments(frm, arrItemCode);
            });
	}
});